Archive for the ‘Female Genetics’ Category

Elad Gil is running around the Color Genomics office when I come to meet him for a little sit-down. The place is full for a Friday afternoon. Theres a worker taking calls on the couch in the front and plenty of others pacing about in the background.

The office is tucked away in an unassuming industrial area of Burlingame, California, in a building that reminds me of some 60s-style government structure. Color is easy to spot: First suite on the first floor and the only one with, well, bright color.

Gil offers me a water and we sit down in a little conference room. Jokingly, he says maybe he can do something funny for the featured image for my article like pretend to hold up the color wheel logo. Katie would never let me do that, he says, referring to his chief marketing officer and ex-Twitter employee Katie Jacobs Stanton. Hes nerdy funny. I like that.

Gil came to Silicon Valley with impressive academic credentials, including a degree in mathematics, another in molecular biology and a PhD in biology from MIT. It was 2001, and he had hoped to make a dent in the universe. But the timing was off. The country was already headed toward an economic downturn, then 9-11 happened.

He was at a telecom company that quickly grew to 150 people and shortly after shrank to a tenth of the size in five rounds of layoffs. Gil was cut in the third round.

That was a turning point for him.

All these people helped, he said. Like big brand-name VCs were referring me to companies just to help. They were like, Everythings collapsing. Youre some random person who showed up with a PhD in biology. You have no job prospects.

He went on to hold prominent positions at Google and Twitter and now as a co-founder in Color Genomics. Hes also an investor in several well-known startups, including Airbnb, Square, Stripe and Pinterest, and is in a position, which hes known to readily use, to give back to Silicon Valley in much the same way.

But, a dark cloud has been hanging over the Valley lately. News of several incidents of sexual harassment and sex discrimination of female founders have toppled VCs once seen as demigods and caused some to lose hope in the dream.

SB: Ive heard people say Silicon Valley is over. Theyve kind of almost lost faith in their heroes, and then theres all these other little pop-up satellite Silicon Valley-esque cities starting to come up. Do you think Silicon Valley is over?

EG: Oh God, no. I think its best days are ahead of it Do you know the last time they said that Silicon Valley was over?

SB: When?

EG: Theres two times.One was in the early 90s where they were like Its over. Theres nothing left to be done.

SB: At the height of the semiconductors.

EG: Yeah, because all the semiconductor stuff was really sort of like 70s and 80s. And then in the early 90s 91, 92, 93 theres the internet. And I was talking to somebody who was really prominent in the internet wave, and he was like I moved out here in like 93 and everybody thought it was over.

Literally, that was the thing. They were like The best times are behind us. All the stuff that could be done has been done. Its over. And then a small group of people were like, Lets do stuff on the internet. Others were like Thats insanity. Like the internets a stupid toy thing that connects five universities. Who cares? Then of course, Netscape happened, and then theres a wave of innovations, and then in the bubble that I moved into with my perfect bad timing, the collapse I moved into. In that period, everybodys like Oh, theres nothing interesting on the internet, and we have to go back to hard tech. And Kleiner Perkins got into clean tech, and all these people were talking about nano tech, and it was like Silicon Valley is over, and theres nothing to do. We need to find new industries. Thats literally what happened.

Then all the social waves happened, and the mobile waves happened Just like theres a business cycle, theres a venture cycle, and innovation cycle. You end up with these gaps, and I think were just going through a period where theres less obvious things.

Interjection: We started talking about cryptocurrencies, ice cream, health tech and whats next in Silicon Valley. Ive cut a bunch of this short for brevity.

EG:I basically think the last six months have been cryptocurrencys Netscape moment, and I think were still trying to figure out whats Google, and whats PayPal, and Yahoo, and what to keep in with this first wave.

SB: [Cryptocurrency] scares people, especially when its very new.

EG:Totally. You remember the first internet. People were like Oh, nobodys going to buy anything on that. Theyre not going to put a credit into a website. Thats madness.Now weve got Instacart, Amazon

Can I say something, and then argue that I never said it when you have a tape? Can I do that purposefully?

SB: Okay. What do you want to argue?

EG: I never said I like chocolate ice cream. I like chocolate chip, or something like that.

SB: And Ill be like No, on the record. This is where he said it.

Okay, so kind of wrapping this up. Where do you see Color fitting in all of this?

EG: Yeah. I think Color was sort of part of a very early first wave of the visual data area So really our focus is on how do you unlock information thats sort of locked up for people, make it something they can actually use to help manage their own health.

SB: People might say it makes it a lot harder if you have to go through your physician first to get this information. I think thats kind of the allure of these at-home health tests a lot of the time.

EG: I think it depends on how much friction you can take out of the physician process, but also the flip side of it is, if physicians are telling people that they should consider it, thats actually a really powerful way, as well, for people to participate. So I think there are sort of two sides of the same coin.

As an Ashkenazi Jew, I remember going to my doctor and like Hey, should I be taking these genetic tests for cystic fibrosis and Tay-Sachs and all this other stuff as a carrier? And he was like, Oh yeah. Youre Jewish. Sure. You should do it.

SB: Sure. Gotta be proactive.

EG: But I had to bring it up, right? Its something thats often recommended for Ashkenazi Jews to do. So, were basically trying to create an online version of that, where youre still working with the physician but theres different ways for you to work with him.

SB:Where do you think people can innovate further in the health tech space right now? What would you like to see?

EG: Yeah. Um, thats a great question. I think ultimately, theres so much data available ambiently through peoples bodies This company Cardiogram that I mentioned. Im a small investor there, from a disclosure perspective. Thats a good example of where youre just ambiently recording and then telling people that they may have had a heart attack. I think that those are some themes that are really intriguing.

I think the top part in healthcare is that the people who are often benefiting the most from things arent necessarily the people making the buying decisions. There are some things at a low enough price-point, so that really changes the adoption rates of different tested products. Thats one obstacle, in terms of larger-scale adoptions.

SB: Okay. I think well end it on that.

The rest is here:
Elad Gil and Silicon Valley's bright future in cryptocurrency, genetics and health tech - TechCrunch

The Mary Sue

Orphan Black Science Recap: Guillotines Decide The Mary Sue Welcome to our Orphan Black science recaps, where Casey, a graduate student in genetics and developmental biology, and Nina, a professional science communicator, examine the science in each episode of OB and talk you through it in (mostly) easy-to ...

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Orphan Black Science Recap: Guillotines Decide - The Mary Sue

VETERAN Queensland Brahman breeder Alf Collins Sr was saluted by his peers recently when he was awarded the 2017 Helen Newton Turner Medal during the Association for the Advancement of Animal Breeding and Genetics conference in Townsville

Alf Collins receives his Helen Newton Turner Medal at the 2017 AAABG conference in Townsville

With almost missionary zeal, Mr Collins has followed a lifetime crusade of breeding fertile, functional Brahman cattle at his Collins Belah Valley Brahmans enterprise near Marlborough in Central Queensland.

The AAABGs medal, established in 1993, honours the memory of outstanding CSIRO livestock geneticist, Helen Newton Turner. It is awarded to provide encouragement and inspiration to those engaged in animal genetics. The medallist is chosen by trustees from the ranks of those persons who themselves have made an outstanding contribution to genetic improvement of Australian livestock.

Building on the foundations established by his father, Alf Collins Snr has applied dedication, careful recording and rigorous focus on breeding for profitability, to the continuous improvement of Brahman cattle in the CBV herd.

He says Brahman cattle have to perform in very challenging environments, and breeding programs to deliver genetic improvement in those environments are challenging too reflecting large scale of operations and variable climatic conditions.

Mr Collins has met these challenges head-on and collected performance records underpinning reliable EBVs and used the information backed by hard-nosed practical understanding of functionality and survival ability, to generate impressive genetic progress over a number of decades.

Perhaps the most outstanding aspect of that genetic progress is the substantial progress in female fertility a trait considered challenging among breeders of tropically adapted cattle world-wide. CBV has actively participated in industry R&D, including significant contributions to the Beef CRC programs I, II and III.

Mr Collins is a deep thinker about what cattle need to do in the tropical environment, and has never been afraid to try novel approaches or include new traits if they will help breeding cattle better and better suited to the environment and to improving profit, AAABG said in its commendation.

He continues to be an outstanding pioneer and innovator in real-world application of genetics technology, and the demonstration that it is possible to breed genetically fertile, productive and profitable tropically adapted cattle is an inspiration.

Published below is Alf Collins acceptance speech delivered during the AAABG conference in Townsville:

Genetics, management, and speed.

All thanks be to God, for all the cattle, people and opportunities that He has put in our path.

Today, part of that thanks is to the Helen Newton-Turner Trust that has chosen to honour me with this medal of recognition. This is beyond my understanding or expectation to be honoured by such eminent and worthy scholars.

I intend to honour some of the wonderful people and livestock with which God has guided and stimulated my brief road in management, genetics, and thinking.

Wind beneath our wings comes in many forms and directions.

RB McNaught in primary school was inspirational; Rodney M Deeth could teach me Maths B and make the theorems so interesting and challenging. I still keep in touch with him. I left formal schooling aged 13, and raced into the realities of commerce and genetics.

In 1966, George Starritt and family employed me, and inspired me with their progressive breeding of sheep. 1967 I travelled alone into Middle East, Europe and Latin America, thence to USA.

At all times, I had a quest for people and pathways of excellence.

In Britain, Yorkshire yielded Harry Morrell, measuring and breeding Friesians based on cost and net yields. At that time when gross mass of milk cows was sweeping the world irrespective of cost, Mr Morrell had chalk boards above every cow, and scales and milk testing, hunting for efficiency and genetic answers. He found them, with the result that his Friesians were the size of robust Jersies. His results were extraordinary, and he treated me like a son. The resolute James McGowan in Scotland proved all things were possible with determination, thought and hard work.

Steve Abecasis in Venezuela, many others through Latin America, lead me to Harry Gayden in Houston, and Jack Garrett, as guides and mentors. At every stop-over there were volumes of inspiration, in useful things to do and mistakes to avoid.

I sought Dr Max Hammond, a graduate of LSU, past manager of Brooksville Research Station, who was president of Performance Register International, and managing Bill Stuarts Brahman herd of roughly 600 cows. He was seeking fitness for function in a breed and an age that was not fashionable and without the tools of today that we employ. Dr Hammond was always aiming high, with disciplined management , cattle and matters of faith. He was hugely successful, in my mind.

Through Dr Hammond I attended a short-course at University of Florida, Gainseville, where some of my heroes of research and extension operated.

The trio of Dr Tony Cunha, Dr Marvin Koger, and the resolute Dr Alvin Warnick were in full flight. They were so practical, and so competent in communicating in both directions with cattle ranchers, exhibiting in themselves fitness for function in every way. My father engendered in me a hunger for published research bulletins, as did his brother , Harry. Those Florida guys were right in there, with some from LSU, Texas A & M, and our CSIRO.

At the age of 88 years Dr Warnick mentioned to one of his early students, Bob Crane who regularly looked in on Dr Warnick, that he really wanted to go to Australia to CBV to explore first hand what he had read and heard about our methods and goals. He figured that he was really too old. Bob Crane left his house and promptly booked tickets for his old Professor. We were honoured and inspired. At every stop, as we travelled, Dr Warnick had some more questions and challenges penciled in his notebook. We had a great morning at Rendall Laaboratory, in Rockhampton, including retired and current researchers. Greig Turner and Doc Warnick were the elders, and lit right up in discussions.

The benefits of Dr Warnicks pondering have enormous value, and continued personally right up to his death earlier this year.

Larry Cundiff was always wonderful with his open doors at Clay Centre, to his fine teams of thinkers. Cattlemen such as Paul Genho, Tom Lassater, Steve Radakovich, Robin Giles, Kit Pharo, Gregg Simonds, and many others have been so encouraging in mentoring, by example, in discussion, and debate.

I never met Dr Bob Taylor, but many of his past students carried his legacy to our door. Thank God for all those links.

A common thread in most of these wonderful people was an awareness of the burning need to search for commercially relevant traits on a low cost, high expectation level.

From the late 1950s my father took me to CSIRO, and short courses on management and genetics. We were richly blessed to have Belmont research station on our doorstep. Dr RB Kelley was a byword in our home. His books were read time after time, and when I called to visit him in retirement he received me like a son. He showed great courage in the face of powerful opposition as he selected cattle and sponsored early research on Zebu cattle in Australia. CSIRO had an amazing culture in those days, hallmarked with spirited debate, kindness, generosity, intellectual agility, and courage. Dr Turner, Dr Vercoe, DOcchio, Frisch, Seifert, ONeill, all carried the flame for betterment. UQ had Professor John Francis, Professor Ray Johnson, Professor Butterfield from University of Sydney; they always inspired. UNE seconded Dr Hans Graser from Germany to lead the new generation of analysis, and his teams are now legendary. Across the street, another legend in UNE, Jack Allen at ABRI took the commercial product to cattle breeders, and has worked tirelessly to keep the mathematics of Breedplan relevant to animal breeders and skeptics alike.

Jack Allen and Peter Speer were the keys for us to develop Brahman Breedplan, using the existing Flekvieh/ Simmental database, and then when we were given years of back-data from CSIRO and the UQ Gatton herds, our previous collaborations really yielded fruit. Ken Rowan and Chris ONeill were monumental in their efforts to have this done.

Earliest breeders of these humped adapted species had those same qualities, full of encouragement and thought.

Lionel DeLandelles stood so tall, with Maurice DeTournouer, and then Ken Coombe, in the pioneer days of adapted cattle. In their day, they measured what they could, illustrating what was possible with adapted cattle. There were simply no insurmountable obstacles, to these courageous friends and mentors.

Then came Dr Michael DOcchio, and Dr Jim Kinder right into our stockyard, to continue their research in reproduction. This was a great leap forward, and the last 30 years have been illuminated by all the great minds they sponsored over our threshold, and their continued stimulation. Wonderful men of science.

That lengthy preamble of the fine folks that inspired my youth was probably necessary, in order to effectively lead us into the realm and integrity of Professor DOcchio.

By his good grace, we have been introduced to higher research, and are now working on a project with Professor Ben Hayes and Professor Mike Goddard.

Reproduction and survival has always been our CBV focus, at a low cost of production.

This is rarely addressed in academic pursuits, and there lies the rock that fractures our links of science to application.

Most research stations around the world operate at a cost per kilogram that the average cattleman would choke on. It is too easy.

The take home message is that inspirational scientists in my world communicated freely with outstanding managers of livestock and land. They actually knew about cost of production, and the harsh blowtorch of economics and profit and loss. That gap needs attention, and nurturing.

This does not exempt cattlemen from making every effort to capture the essence of research, and adapting it to commercial reality.

That essence of scientific research has been the wind over our wings at CBV.

One of my heroes, Dr John Vercoe illustrated this to me with his chart of the effect of environmental stress on growth heterosis. As costs go down, stress increases, and heterosis evaporates.

That was a bell ringing revelation. John Vercoe was amazed that more cattle breeders did not understand stress and heterosis, and more so, that the importance of reproduction was not registering in genetic selection. Vercoes facilitating DOcchio and Kinder into our herds and our present thinking showed courage and great foresightwind for our wings.

Reproduction speed and survival can almost exclusively direct financial survival. Never underestimate the role of truly adapted cattle in this hunt for reproduction. Most of the land mass of Australia, and in fact most places in the world where beef cattle graze, can be greatly augmented by adapted genotypes selected for reproduction and survival at low cost.

Our management template of breeding cattle is based on rigor and transparency, and I have caution about genetic predictors without rigor, and stressors, in the field.In all the complexities of science and nature, we know it is a simple goal; we also acknowledge these proposals are neither easy nor simple.

At CBV we are dedicated to the hard yards of unraveling complexities with cash and kind, not at all daunted by the skin we can lose in this game.

Our philosophy does vary from most seedstock operations in the reality that we operate just like our best clients at a low commercial cost, with no expensive sale-stock packaging, and we do not seek a flamboyant sale of psychological bidding shoot-outs. We are simply hunting for profits for our clients on capital invested , inside their barbed wire. Those clients in turn, have supported us.

Our core clients all over the world, who ran with us in trying our new management templates and genetics, also provoked us, and helped us fund our dreams and explorations whilst buying bulls or semen.

Thank you for this honour of the Helen Newton Turner Medal. I am deeply touched by how I have been welcomed into such a wonderful group of scholars.

Long live the curious mind.

Read more from the original source:
Genetics honour to CQ Brahman breeder Alf Collins - Beef Central

MOST of Australias significant beef breeds are expanding, with increased seedstock registrations despite Australias overall beef herd sitting at a 20-year low at just under 26 million head.

Figures released during last weeks Australian Registered Cattle Breeders Association annual general meeting indicated a nine percent lift in registration numbers in 2016 compared with the previous 12 months in primary registers. There was a 6pc lift when primary* and secondary registers* are combined.

In total, 2016 total registrations at 211,781 were second only in number to 1995, when a little over 213,000 primary and secondary registrations were made. (see graph below).

Primary registrations in purple, secondary registrations in red. Click on image to enlarge

Judging by seedstock registrations last year, the growth of the Angus breed continues unabated.

As the graph of the ten largest breeds by registrations published below shows, Angus again topped the list, recording 50,096 registrations back in 2007 and 70,076 in 2016, an increase of 19,980 or 40pc over the past decade. Year-on-year, Angus registrations rose 7pc in 2016.

Angus Australias Andrew Byrne said the breed now had a registered female inventory of more than 100,000 to produce this years figure of 70,000 registrations. A back-of-the-envelope calculation delivers a $2 million return to Angus Australia based on an average female inventory fee of $20 per breeding female per year. Mr Byrne indicated that 30 staff now populate the recently expanded Angus Australia office in Armidale NSW where they have developed many income streams to fund operations.

There was a time 40 years ago when the Murray Grey society had more staff, more members, more registrations and more money than the Angus society. However Murray Greys have increased registrations from 2015 to 2016 and now sit in 11th spot in the breed hierarchy based on registration numbers of 5122 in 2016.

Click on table image for a larger view

As stated previously on Beef Central however, seedstock registrations or numbers of bulls sold at auctions are in fact poor indicators of overall breed popularity across Australia. Its is frequently estimated that up to two-thirds of all Brahman bulls used in Australia, for example, are not registered animals at all, but unregistered herd bulls bought out of the paddock, or bulls in fact bred on the property on which they are used, drawn from internal purebred nucleus herds.

In percentage terms, Wagyu continue to perform strongly in registration numbers, lifting another 21pc over the past 12 months to register 10,261 head. Over the past ten years, the growth in registrations has been meteoric, lifting 178pc more than twice the rate of the next fastest growing breed.

With registered Wagyu seedstock now bringing exceptional prices as the demand for bulls increases, a Wagyu content test has been developed allowing conforming cattle to achieve purebred status (but never fullblood) and enter the primary register.

A grading-up register is also planned for percentage Wagyu. AWAs Carel Teseling indicates hundreds of new cattle being readied for entry in these registers while industry sources suggest these numbers could be in the thousands.

Sitting in second spot behind Angus for registrations this year is Hereford with 25,257 new registrations in 2016. This is an increase of 8pc on the previous year, but down 19pc on 10 years ago when perhaps there were some dual registered (horned and poll) skewing the numbers.

After a time of internal bickering, Herefords Australia has a new president, Bill Kee, some new board members, a new general manager Andrew Donoghue and a leading animal scientist Alex Ball all poised to take the breed forward. Commanding second spot on Australias registration ladder, the breed has a good launching pad. An industry source also claims the large financial losses Herefords Australia was reported carrying are nowhere near as high as earlier indicated.

In the third, fourth and fifth positions for registrations in 2016 are the three major tropical breeds Brahman, Santa Gertrudis and Droughtmaster, all with numbers to continue their significant contributions to the sustainability of the northern industry.

Brahman numbers have not changed much in the past 10 years (down 3pc to 24,449 this year), Santa Gertrudis had a big jump (up 22pc to 17,423), while Droughtmaster declined (down 27pc to 11,386). Worth noting, however, is the difference in approaches in different breeds to registration (more on this below). The Droughtmaster breed, for example, has no secondary register, and has only this year commenced introduction of calf-recording for females. Both have a big impact on registration numbers.

The Brangus breed is the smokey in the 2016 report. With 6675 registrations for the 2016 year, it lifts the breed to eighth place following a 56pc jump in registrations in the past 10 years and 45pc since 2015.

According to the Brangus Associations president Mark Beckman, the breed now has more members registering more cattle with many using the foundation register to bring in top Angus and Brahman genetics while keeping within the 25pc to 75pc range for either parent breed content.

However, most registrations are cattle derived from parents that are registered Brangus. The breed will be on show at the 12th Brangus bull sale at Roma Qld when 164 will step into the sale ring on September 1 (see full list of upcoming spring bull sales for all major breeds here).

The breed continues to attract new members who are registering more cattle and the commercial attributes of the breed are drawing cattle producers towards it, Mr Beckman said.

The Ultrablack, an Angus-heavy Brangus-type, does not appear in the breed lists but some are registered in the Brangus foundation register and some in the Angus Multi-Breed (MBR) register.

For several decades ARCBA has provided registration statistics to assist industry to plan and develop strategies for growth and breed improvement. These reports are made more difficult with several different systems in use in the Australian industry.

Some breeds use the annual female herd inventory system where members peruse their lists annually, deleting females that have died or no longer worthy of retaining in the stud herd, and pay an annual fee averaging around $20 per retained female. Their progeny can be registered in the various herd books.

Other breeds retain the traditional method of registering and paying a fee for a calf once it is born with penalties to register these calves later in their lives.

Some breeds, such as Santa Gertrudis, have a system with physical inspection by an independent breed association employed classifier necessary before herd book registration can be completed.

Since 1998 the ARCBA report has included two levels of registrations, primary and secondary. In general terms, primary registers are the highest level of pedigree authenticity, many are closed herd books while some cover cattle that have been graded up to fourth generation of greater than 95pc breed content.

Secondary registers are for cattle where registrations have lapsed and are being brought back into the system and for cattle involved in the grading-up process from other breeds.

ARCBA describes secondary registers as those which include animals that are bred for seedstock production and recorded by a beef breed society but excluding animals entered in the societys herd book. The Association describes seedstock production as The production of bulls for use in the registered and commercial cattle sectors.

For example the Angus primary register is the Angus Herd Book Register (HBR) and is a closed herd book i.e. both parents must be in the HBR. The Angus secondary register is the Angus Performance Register (APR) which allows members to record pedigree and performance information on non-HBR straight bred Angus cattle.

The inventory fees for HBR and APR females are the same (around $20/female average). Last year 45,117 Angus entered the HBR and 24,959 the APR. There are no accurate figures, but industry sources suggest that commercial bull buyers do not show a preference for HBR over APR animals.

Figures quoted in this article combine primary and secondary registrations.

Over the years breed organisations have threatened to withhold their registration statistics from ARCBA if breed comparisons were made.

Genetics Central believes it is in the interests of the industry to have access to this information to facilitate planning and monitor industry-wide trends.

Maybe a potential new seedstock producer may decide there are too many Angus calves being registered (70,076 in 2016) creating an over-supply perhaps encouraging them to go with a promising smaller breed such as Speckle Park, where only 1053 calves were registered in 2016 but demand is hot.

Follow this link:
Weekly genetics review: Registrations on the up for most beef breeds - Beef Central

As federal wildlife officials review the endangered status of the Florida panther, one scientist's work has been singled out as a focus: geneticist Melanie Culver.

In 2000, Culver and three fellow scientists published a study of the genetics of big cats that concluded that all the panthers, pumas and mountain lions in North America are actually a single sub-species.

In other words, according to the Culver study, Florida panthers are nothing special, genetically. They're just another big cat in a nation that contains thousands of them, some of which are already hunted. If the U.S. Fish and Wildlife Service adopts that point of view, it could lead to taking panthers off the endangered list.

But Culver, in an interview, said she believes the Florida panther still belongs on the endangered list -- just not the way it's listed now. The U.S. Geological Survey scientist concedes that making a change would require a complex solution.

"You'd have to de-list it and then petition it to be listed as another entity," she said. "That's a legal problem. They'd have to completely lose legal protection to be protected the right way."

Florida panthers have been listed as endangered ever since the first endangered species list was drawn up in 1967. They are also Florida's official state animal, voted in by schoolchildren over such other contenders as the alligator and the mosquito.

They have long been considered a distinct sub-species of the puma that roam wilderness areas of North and South America. At one time, scientists believed there were about 30 such sub-species.

Federal rules require the agency to review the status of each endangered or threatened species every five years, and the wildlife agency has announced that it's time for that routine review. But one aspect of the review won't be routine.

"One of the most interesting things we're going to review is the taxonomy," said Larry Williams, South Florida field supervisor for the federal agency. He specifically cited the Culver-led study as something that the agency will consider.

Questions have been raised for years about whether the Florida panther is really a distinct sub-species of the pumas found out West. The questions took a different turn after 1995, when state officials tried an unprecedented experiment to save the panther from inbreeding and genetic defects by bringing in eight female mountain lions from Texas to breed with them.

The cross-breeding saved the panthers, and sparked a baby boom. The panther population, estimated to number no more than 20 to 30 in the mid-1990s, now is estimated at around 200.

But it has raised questions among Southwest Florida residents about whether those are still Florida panthers and whether the state's estimates of the population are correct. Meanwhile some have cited the Culver study as an argument for eliminating their endangered status.

"There are tens of thousands of them throughout North America, they are overpopulated and legally hunted throughout much of their range," outdoorsman Mike Elfenbein of Port Charlotte, who helps run the "Panthers of South Florida" Facebook page, wrote in a 2015 letter to U.S. Rep. Vern Buchanan, R-Sarasota. "The 'Florida panther' is not now, nor was it ever in danger of going extinct."

But not everyone agrees wholeheartedly with the Culver study. Dave Onorato, a biologist with the Florida Fish and Wildlife Conservation Commission's panther study program, said one shortcoming is that the study used a small number of samples for the panthers.

He noted that when the state has done its own DNA tests, using an approach different from Culvers, "the panthers still cluster as their own sub-set, away from the Texas and Western sub-sets."

Elizabeth Fleming of the Defenders of Wildlife's Florida office contends that without a scientific consensus backing the Culver study's findings, the Fish and Wildlife Service should not change the panther's status.

"It is a native ranging animal, and we think it deserves a place in the Florida landscape," she said.

To Culver, though, the problem is that the panther should not have been put on the endangered list as a sub-species of puma. Instead, she said, panthers belong on the list as what's known as a "distinct population segment" of the puma.

In other words, the fact that this population of panthers is the only colony of pumas east of the Mississippi, and it's largely confined to the southern tip of Florida, still qualifies them as endangered, in her view.

While 200 panthers is an improvement, she said, it "isn't what we would consider sustainable. That's not great." Over time, genetic defects would creep back in, putting them back on the road to extinction, she said.

Whether the Fish and Wildlife Service follows Culver's advice is unknown. Williams wouldn't speculate on the outcome of his agency's review this week, except to say it would follow the latest scientific findings.

Four months ago the agency announced it was lowering the protection level of another famous Florida critter, the manatee, from endangered to threatened -- despite the objections of a majority of the public that commented on the move, as well as the scientists who had been asked to review it.

Senior news researcher Caryn Baird contributed to this story. Contact Craig Pittman at craig@tampabay.com. Follow @craigtimes.

Geneticist says Florida panther still deserves endangered species protection 07/08/17 [Last modified: Friday, July 7, 2017 4:15pm] Photo reprints | Article reprints

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Geneticist says Florida panther still deserves endangered species protection - Tampabay.com

CRISPR has ruffled feathers, but it may be capable of saving species

Frans Lanting/National Geographic Creative

By Adam Rutherford

KAKAPOS are fat New Zealand ground parrots that have stared into the abyss of extinction for decades. Conservationists have laboured to raise numbers from the moribund low 50s to a still ultra-critical 160 or so today.

Once a species becomes so depleted, however, a lack of genetic diversity can hinder its long-term salvation. A geneticist once told me of a crazy idea that might save the kakapo. He said that there are more stuffed kakapos in European museums than there are living birds. If we could extract DNA from those dead parrots, from a time when their numbers were large, we could genetically engineer the living birds to mimic the once healthy species by changing single letters of genetic code.

There are a lot of ifs here, but the modification of DNA itself even at the level of precision this mad scheme would require is eminently possible, thanks to a technology known by the acronym CRISPR. Ten years ago, identifying, characterising and modifying a gene then getting it back into an organism was a process that took weeks, months or years. With CRISPR you can perform the same process in days.

Incredibly, it looks as though CRISPR will live up to its hype, transforming every aspect of biology as genetic engineering did from the 1970s on. Tweaking individual letters of genetic code, it takes just hours to finely edit what evolution fashioned over billions of years. All aspects of the science of life are within CRISPRs reach: disease, conservation, synthetic cellular manufacture.

CRISPRs complex origins as a gene editing tool can reasonably be credited to a few key players: Jennifer Doudna is one of them. With her former colleague Samuel Sternberg, she has written a detailed account of the story so far. It may well end up being compared with the book that inspired a 12-year old Doudna in the first place: James Watsons The Double Helix.

But while Watsons iconic account of his and Francis Cricks discovery of the structure of DNA is dramatic and myth-making, bitchy and sexist, A Crack in Creation is thoughtful and thorough. Packed with amazing female scientists, it is thrilling, generous and no less personal. Its a good tale of how science works, tracing all the meandering paths that lead to discovery: meetings, chance encounters, ceaseless discussions, and the endless beavering of lab life.

Concern about genetically modifying people may once have seemed overheated. Thats about to change

A Crack in Creation is quite technical at times, and a touch bogged down with the clinical specifics of the many diseases that CRISPR may one day fix. The journey from the days of gene therapy to the first human CRISPR studies in China is no amble, either. Following these early Chinese studies, Doudna recommended an instant moratorium on human CRISPR experimentation. Similar moratoriums were called for in the first days of genetic engineering in the 1970s, and in recent years, following the experimental modification of virulent flu viruses.

Public concern about the genetic modification of people may have seemed overheated while we lacked the scientific chops to do anything significant. But that is about to change: CRISPR is powerful and potentially scary. Doudnas own ethical position comes into focus in the final chapter. Its a nuanced account, but she definitely inclines towards excising conditions like cystic fibrosis and Huntingtons disease from the human germ line.

A Crack in Creation touches the surface of these issues. It doesnt delve deep, but one book cannot do everything. Genetics has been in perpetual revolution for several decades now. Since the 1990s, when the Human Genome Project ground into action, there have been so many advances in our understanding of genetics and our ability to manipulate DNA that its hard to keep up. Doudna accounts for the many cracks in creation in the 21st century: developing RNAi, where genes can be silenced with tiny bits of ingested genetic code; the building of giant chromosomes to help us clone larger genes; and the manipulation of stem cells. All of these achievements resulted in Nobel prizes Doudnas must surely come soon.

We need scientifically informed public conversations about what we should do next with these powers, and Doudnas book is a good place to begin. The first gene engineers of the 1970s framed their discoveries by actively engaging with the ethical, legal and political ramifications of genetic engineering. So must we. As I write this, says Doudna, the world around us is being revolutionized by CRISPR, whether were ready for it or not. So strap in and get up to speed, because these days, the science of modifying life moves pretty fast.

This article appeared in print under the headline This changes everything

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ESPN senior writer Peter Keating joins OTL to share his findings on concussions in female athletes, featured in ESPN The Magazine and on espnW.com.

This story appears in ESPN The Magazine's Body Issue 2017. Subscribe today!

EVERY FOUR YEARS or so, some of the world's most prominent scientists gather to synthesize and summarize the latest in brain-injury research. Since first meeting in 2001, the assemblage, called the Concussion in Sport Group, has grown in size and influence. Doctors, athletic trainers and media types around the world take their cues from the recommendations it publishes and from the Sport Concussion Assessment Tool (SCAT) it has developed. When members gathered in Berlin last October, Jiri Dvorak, then FIFA's chief medical officer, said they worked on behalf of some 1billion professional and amateur athletes. For that 2016 symposium, around 400 medical and sports professionals met in the Grand Ballroom of the Ritz-Carlton hotel, with art nouveau stylings that hark back to the days before the world wars and trappings so posh that guests enjoy breakfast honey harvested from a rooftop beehive. Over two days, a stone's throw from where the Berlin Wall used to stand, the leading lights of the sports neuro-establishment made clear their role as gatekeepers of concussion research. Organizers closed the conclave to the media and swatted audience members off social media.

There was another group almost entirely shut out of the 5th International Consensus Conference on Concussion in Sport: female athletes.

Of the dozen sessions at the conference, not one was dedicated to sex or gender. Researchers made 24 oral presentations during the meetings; one focused on female athletes. Among the 202 research abstracts, nine, or less than 5 percent, studied women specifically. "Gender hasn't been a hot, hot topic," says one member of the Concussion in Sport Group.

Hot or not, the facts the conference could have displayed are shocking. Women suffer more concussions than men in the sports that both play, with an injury rate 50 percent higher, according to the most recent research. Female athletes with brain trauma tend to suffer different symptoms, take longer to recover and hold back information about their injuries for different reasons than males. Anyone involved in sports should have a grasp of these key facts. Yet the leading national and international guidelines for understanding sports concussions and returning injured athletes to play ignore key differences in how women and men experience brain injuries.

Here's what's even more stunning: All of that information was public knowledge eight years ago, when ESPN The Magazine first looked at the subject of concussions and female athletes ("Heading for Trouble," March 23, 2009)-and all of it is still true. The latest studies continue to find that women get brain injuries more often in sports also played by men. But research into why and how is lagging to nonexistent, as are efforts to reverse the trend. Which means millions of female athletes are putting their brains at risk unnecessarily.

"More and more of the athletes I have seen over time are young women, and I've found they get less information about concussion from their coaches, and from the media too, than men," says Jill Brooks, a clinical neuropsychologist who runs Head to Head Consultants in Gladstone, New Jersey, and who in 2004 conducted one of the earliest research reviews of sex issues in brain injury. "They are struggling to deal with their particular symptoms and often not being taken as seriously as they should be. The sports world is much more accepting of girls and women as athletes but still gives the topic of their concussions short shrift."

FEMALE SPORTS SCIENTISTS pioneered the initial research into sex, gender and concussions more than a decade ago. Dawn Comstock, a professor of epidemiology at the Colorado School of Public Health and a 4-foot-11 former rugby player, started tracking injuries among high school athletes in 2004 and began reporting sex differences in brain injury in 2007. In May 2016, she told the House Energy and Commerce Subcommittee on Oversight and Investigations: "In gender-comparable sports, so sports that both boys and girls play, by the same rules, using the same equipment, on the same fields, like soccer and basketball, girls have higher concussion rates than boys." Tracey Covassin, professor of kinesiology at Michigan State and a certified athletic trainer, has been studying college sports since 2003, with similar results.

But when it comes to looking deeper into the experience of concussions among female athletes specifically, researchers for the most part have been uninterested, unwilling or unfunded. The frontier of knowledge has been stuck for years in epidemiology-studies, again and again, of who encounters a health problem in the general population and when, rather than how and why it strikes a particular group. "There's a huge gap in the science of brain injury," says Angela Colantonio, director of the Rehabilitation Sciences Institute at the University of Toronto. "There has been a lack of explicit consideration given to sex and gender. We're just starting to scratch the surface."

A major problem with concussion research is that very few people conduct it who don't have a stake in its outcome. I think these folks didn't want to see their names used in lawsuits.

Katherine Snedaker, clinical social worker

In the 2017 Consensus Statement on Concussion in Sport, which 36 of the scientists who met in Berlin published in April, and which runs more than 7,000 words, "gender" never appears and "sex" only once. It's just one item on a laundry list of factors, such as age, genetics and mental health, that the document notes "numerous studies have examined" for their potential impact on how athletes heal from concussions. The consensus statement doesn't actually evaluate what such research has discovered about the effects of sex or gender, except to say there's "some evidence" that teenagers "might be" most vulnerable to persistent symptoms, "with greater risk for girls than boys."

Several Europe-based contact-sport federations fund the meetings of the Concussion in Sport Group. FIFA, the International Federation for Equestrian Sports, the International Ice Hockey Federation, the International Olympic Committee and World Rugby split the costs of the Berlin conference, totaling approximately 250,000 euros (about $284,000), according to two sources at the group. Any of those organizations could be threatened if evidence emerges that it should have managed repetitive blows to the head better among particular kinds of athletes, such as adolescents or repeat concussion victims-or females. And the 30 co-authors of the consensus statement who filed conflict of interest disclosures declared 132 potential entanglements among them. All of which has some brain-injury research advocates concerned that the authors might have hedged their conclusions to avoid exposing their patrons to financial or legal liability. "The statement is extremely disappointing," says Katherine Snedaker, a clinical social worker in Norwalk, Connecticut, and founder of the research and advocacy group Pink Concussions, who attended the Berlin conference. "But a major problem with concussion research is that very few people conduct it who don't have a stake in its outcome. I think these folks didn't want to see their names used in lawsuits."

Even one of the consensus statement's co-authors echoes this criticism. "A lot of intelligent brains have been added to the committee," says Robert Cantu, professor of neurosurgery at Boston University and a founding member of the Concussion in Sport Group. "But I think some are so happy to be part of all this, sometimes they don't look hard enough at the research. And you've got to ask if that serves as a huge protective force for the organizations who put up the money to fund the meetings."

"We reviewed the literature on clinical recovery from concussion," says Grant Iverson, a professor of physical medicine and rehabilitation at Harvard Medical School and co-author of the consensus statement. "We examined many predictors and modifiers. Sex was one of them."

But when it comes to women specifically, the group has a particularly egregious history. Its third consensus statement, published after parleys in Zurich in 2008, included two ambiguous sentences about whether sex or gender influences the likelihood or severity of concussion risk. Four years later, again after meetings in Zurich, the fourth consensus statement also devoted two sentences to females-the same two sentences. Those sentences even cited the same three sources. From 2008 to 2012, women's participation in sports grew rapidly, rising 13 percent in the NCAA alone. Public interest in concussions also exploded, as the NFL crisis reached full tilt. And during those years, about 300,000 females aged 19 or under went to U.S. emergency rooms with sports- or recreation-related brain injuries. Yet the international consensus found nothing new to learn or say.

"The topics we focus on, we go into pretty thoroughly," says one researcher in the group. "Other material, we pretty much don't touch at all. Which is how stuff slides from one year to the next, not only unchanged but not updated."

"It was a cut-and-paste job, down to the footnotes," says neuropsychologist Brooks, who attended two earlier international consensus conferences but was not invited to Berlin.

Andy Mead/YCJ/Icon Sportswire

Facing pressure, US Lacrosse recently adopted standards for women's headgear, but there's little research to inform guidelines.

MOST ATHLETES AND fans have learned about concussions from a decade of reports about former NFL players struggling with the long-term effects of taking blows to the head. As devastating as many of those stories are, the risks of brain injury can get worse the further competition moves from the epicenter of high-stakes sports that is professional football. Lower revenues and remote facilities can translate to poorer medical advice and treatment; scarcer media coverage sometimes means fewer people notice injuries in the first place. And these conditions often apply to women's collegiate sports, where some 214,000 female athletes compete under the regulatory umbrella of the NCAA. DivisionII women's soccer, for example, which Angel Mitchel played at Ouachita Baptist University in Arkansas.

Mitchel took to soccer from the age of 4, playing with her two older brothers in Mansfield, Texas, and dreaming of a pro career. "I would do whatever it took to play," she says. "Soccer was my life."

That all changed on Tuesday, Sept. 13, 2011, when Mitchel, then a sophomore at OBU and known by her unmarried name, Palacios, collided with a teammate while going for a header during a practice drill. The other player's skull crashed into Mitchel's face, knocking her dizzy and sending her to her knees. With her left eye already swelling shut, she lurched to the sideline, where she told her athletic trainer she felt sick. She had already suffered two concussions in high school.

The trainer asked whether Mitchel was dizzy. Was she nauseated? Did she have a headache?

"Yes ... yes ... yes," Mitchel replied.

She says the trainer sent her back to her dorm room with an ice pack. Nobody told Mitchel to see a doctor or checked on her that night. The team gave her an online neuropsychological test the next day, but the results weren't clear because she still couldn't use her left eye. Woozy, sensitive to light and stabbed by migraines, she stayed out of sight as much as she could for the rest of the week.

On Saturday, Mitchel says, her coach instructed her to run laps. She was still sick-she had thrown up earlier that day-and appealed to the trainer, who she says told her: "You don't want to make the coach mad."

I knew I wasn't right, and what was happening was wrong.

Angel Mitchel, soccer player

As Mitchel broke into a trot, the sun burned into her head, vomit swelled again from her guts and pain wracked her whole being every time her feet hit the ground. The intensity and folly of her pain fused into anger. "I knew I wasn't right, and what was happening was wrong," she says.

After a lap around the field, Mitchel stopped and decided she needed to go to an emergency room. Mitchel says that, after that, her coach said she could skip the rest of practice. In fact, he said, she should expect to sit out for a long time.

Doctors found that Mitchel had a severe concussion. She already had recall problems and diminished sensations in the left side of her body. And if she kept engaging in physical activity, she could permanently damage her brain.

Mitchel had a black eye for three months. Her migraines persisted for three years. She never played soccer again. Officials from OBU declined to comment.

Mitchel's experience is an extreme version of what many women experience after sports concussions: isolation, inadequate attention, improper clearance, intimidation. The NCAA for its part has been very late to respond to these issues. It didn't have any guidelines covering brain injury at all until 2010. It required schools to have personnel trained to handle concussions at contact-sports games only because of a massive settlement it reached in 2014. Mitchel, now 24, is justifiably proud of joining the legal action that led to that deal; "I know we have a long way to go," she says, "but it's a great start."

Yet the NCAA doesn't actually enforce how its members implement its new rules. It has never disciplined a school for failing to file a concussion plan or for maintaining inadequate personnel or for returning an injured player to the field. There's still no mention of sex or gender in its best practices for diagnosing and managing concussions or in the concussion fact sheets it distributes to students and coaches.

Maybe the best indication of the NCAA's priorities is simply this: Its chief medical officer has a staff of seven to address college-age health and safety issues from mental health to sexual assault. Meanwhile, its compliance desk has more than 50 employees who police amateurism among athletes.

For all that, Brian Hainline, the chief medical officer of the NCAA, says he has "fire in his eyes" about concussions, and he emphasizes that brain trauma in sports is an issue "much bigger than football." Indeed, in a column on the NCAA's website, he wrote: "We need to spread the word: Yes, female athletes also suffer with concussion, and they may be uniquely predisposed to this neurological event."

It's true that Hainline was close enough to Elliot Pellman, the notorious former chairman of the NFL concussions committee, for Pellman to blurb a book on back pain that Hainline published in 2007. And that in Hainline's early days on the job at the NCAA, it seemed as if he too might simply make excuses for how sports programs were treating athletes with brain injuries.

But Hainline has a touch of the seeker about him, and he has taken to his role as college sports' concussion-education booster-in-chief. His efforts helped create the Grand Alliance, a $30 million project the NCAA and Department of Defense launched in 2014 to study brain injury in student-athletes and cadets and promote concussion education. Over the past three years, the initiative has enrolled more than 28,000 subjects; 1,931 had concussions, and scientists are examining their brains and bodies over time. It's a highly regarded effort, and Hainline is enthusiastic about working with respected partners to assert leadership in brain-injury research. "We all need to take a step back and stop saying nothing is happening," he says. "Cooperation I never dreamed could happen is happening right now. Concussion has brought us to this place of magic."

But while about 35 percent of the athletes involved with Grand Alliance research are female-the largest cohort of women with concussions ever studied-the effort probably won't report anything new that's sex-specific for years, if ever. To see why, it helps to understand why women and men might experience concussions in different ways.

Scientists have known for a long time that women are more open than men about reporting injuries. Recent research shows they don't just describe more symptoms after concussions, they exhibit more too. An important example comes from Shannon Bauman, a sports physician who began studying brain injury after she got inadequate attention for a concussion she suffered playing hockey. From 2014 to 2016, Bauman tracked 207 injured athletes at Concussion North, the specialty clinic she runs in Barrie, Ontario. She found women averaged 4.5 objective signs of concussion, such as poor balance or vision, versus 3.6 for men. They also took longer to recover; 35 percent of females still showed symptoms six months after their injuries.

"Maybe the reason we talk more about our symptoms isn't because we're weak or vulnerable," says Snedaker, a former athlete who went through more than a dozen concussions of her own before becoming an advocate. "Maybe it's because we have more symptoms and they last longer."

Biomechanics might be one reason for that. On average, women have shorter and thinner necks than men and approximately 50 percent less neck strength. In general, that means females have less of a buffer against anything their heads might slam, whether it's a ball, another player's elbow or the ground. Their skulls experience greater acceleration when their bodies whiplash-and it's that motion that jars a brain and leads to a concussion, like scrambling a yolk without necessarily cracking an egg.

Further, different chemicals naturally course through the bodies of men and women. As a basic example, research has shown that fluctuating levels of estrogen leave women far more susceptible to migraines than men, and migraines and concussions seem to cause similar problems inside the brain. It also turns out that, until puberty (when sex hormones start flowing), young boys and girls get concussions at comparable rates and share similar symptoms. Some neuroscientists have wondered about the effects of sex-specific hormones that either stress or shield the brain when it's concussed.

In a series of groundbreaking studies that started 25 years ago, Robin Roof, then a researcher at Rutgers, found that progesterone, a female sex hormone, reduced brain swelling and improved cognitive function after injuries in rats. The implications were huge: Maybe progesterone could mitigate the impact of brain injury. But the subject wasn't studied much again until 2013, when a team from the University of Rochester recorded data on the menstrual cycles of women who went to emergency rooms with concussions. It found that females who were injured at a point in their cycles when their progesterone levels should have been high suffered more symptoms afterward. "That's counterintuitive, because in animal studies, progesterone has a neuroprotective effect," says Jeffrey Bazarian, one of the Rochester researchers. "But concussion might disrupt its production, shut it off and lead to an abrupt decrease in the blood."

That's an interesting theory, but it's speculative. Hormones interact with one another in complex ways. And large-scale clinical trials of progesterone on brain-trauma victims have failed to show any significant benefit. So Bazarian is left with a nagging question: "How can there be such a discrepancy between rodents doing so well with progesterone and what we've seen so far in humans?"

"We can look at reporting, and we can look at neck strength," Brooks says. "But we have got to get to how the brain works in men and in women, which means studying how hormones affect its function."

That, however, is not a subject the NCAA is pursuing in its research. Its Grand Alliance with the Defense Department is on its way to amassing more than 25 million data points from athletes, information that an "advanced research core" will study with sophisticated neuroimaging devices and comb for biomarkers, or substances in the blood that indicate brain injury. But it will not collect statistics on where female athletes are in their monthly cycles, nor will it analyze blood samples for sex hormones. Those are "interesting and important questions," says Steven Broglio, a professor of kinesiology at the University of Michigan and one of the scientists leading the Grand Alliance's research. "[But] no study can address every concern. Hopefully, future research will take on this challenge."

"I understand you have to pick the low-lying fruit first, but five years from now, it's going to be too late to go back and get this data," Snedaker says. "If you're not going to look at what makes us different, then don't put us in the studies."

BEHIND CLOSED DOORS, some women's sports advocates aren't comfortable looking for differences between male and female injuries. Treating male and female athletes differently could revert to stereotypes that women have been fighting for decades-that they aren't up to the challenges of sports or need special pleading or are simply weaker than men.

But medical science has a long history of judging females by male standards, all too often with terrible results. Medical schools typically use men's bodies to teach students about disease, and doctors are more likely to miss or wrongly diagnose symptoms among female patients. The classic example is a heart attack: Women are more likely to feel as if they have the flu than to experience chest pain. And medical research historically has used male subjects to study treatments, producing findings on everything from aspirin to Ambien that didn't apply accurately to women.

Brain injury, then, is one of many examples where even studies that include women almost never come to separate conclusions about them. In 2016, the Archives of Physical Medicine and Rehabilitation reviewed the scientific literature on concussion since 1980. It found that of 221 published papers, just 7 percent of them broke out their data by sex. "Brain science follows society," Brooks says. "Men are making a lot of the decisions about women's health. I've had to conclude that instead of making change from the top down, I have to try from the bottom up, helping one patient at a time [as they] become healthy, informed, strong women."

Sports concussions are an acute case because so much attention and funding has followed pro football. Most obviously, while the NFL's concussion studies have been riddled with junk science and conflicts of interest, the league has helped tilt research toward helmeted sports. Last September it pledged $60 million toward developing new concussion technology, possibly including a new helmet, and $40 million for researching head injuries. And now the NCAA and the DOD are entering the field.

Naturally enough, parents around the country, many concerned about long-term brain damage and CTE (chronic traumatic encephalopathy), have started to demand greater protection for their daughters-even when science isn't ready to tell them just what to ask for. For example, U.S. Lacrosse, facing pressure from alarmed advocates, parents and state legislators, recently adopted its first standards for women's headgear. It's still optional, but helmets must now meet new guidelines-even though the federation doesn't actually have any evidence that the new equipment will reduce concussions. "This is a national experiment," says Andy Lincoln, who conducts research for U.S. Lacrosse. "There is a need for more information on head impacts and exposures in women's and girls sports."

Yes, there is. So what happens next, as public opinion, and soon enough, lawyers, politicians and salesmen, fill the vacuum left by the institutions that govern women's sports and the scientists they sponsor?

"I'm very concerned," Hainline says.

Originally posted here:
Why does it seem like nobody cares about female concussions? - ESPN

Women not only live longer than men, they also appear to be in more robust health. A new hypothesis offers a reason why: it's in their genes.

Women are known to have a lower incidence of cancer men have a two- to five-fold greater risk of developing the disease. Women are also better able to survive trauma, and, according to some reports, don't get as seriously ill from bacterial and viral infections.

In a new paper, researchers from Ghent University in Belgium argue these sex-specific health disparities may be due, at least in part, to tiny pieces of genetic material called microRNAs. The main function of microRNAs in cells is to turn off, or "silence," specific genes. The researchers say microRNAs located on the female X chromosome may give women an immune system advantage over males.

While the researchers' idea is certainly debatable, the paper "raises awareness of how little we consider the influence of sex on immune responses," said Eleanor Fish, a professor of immunology at the University of Toronto in Canada, who was not involved in the work.

Often, researchers who conduct medical studies on people do not analyze their data by sex, and sometimes they don't report the sex of patients at all. Hopefully this will change, Fish said, so that every time a study is done, sex differences are considered, she said.

XX and XY

In humans, sex is genetic: Females have two X chromosomes, while males have one X and one Y. However, in females, one X chromosome in each cell in the body is randomly shut off, or inactivated, while the embryo is developing.

But X inactivation is not a perfect process, and sometimes genes on the X chromosome escape inactivation. In this case, a female ends up with two active copies of a particular gene.

Here is where the researchers think the microRNAs come in. The X chromosome contains 10 percent of all microRNAs in the human genome. The Y chromosome has none. Some of the microRNAs on the X chromosome are thought to be involved in immune system function and cancer development.

If a microRNA did something "good," like help control cell growth, having two copies of that microRNA might provide females with extra protection against cancer. The same would be true for microRNAs that played a role in immune function.

As a real-life example, septic patients (who have widespread bacterial infections) have low levels of a particular microRNA found on the X chromosome, the researchers said.Thus, this particular microRNA may offer some protection against sepsis.

The researchers said they need to do more work to support their theory. For example, it's not known whether microRNAs on the X chromosome "escape" inactivation, they said.

Other factors

The X chromosome is known to contain a number of genes related to health, Fish said, and adding microRNAs to the mix would suggest that the X chromosome is even more important in terms of health differences between men and women.

However, the X chromosome is far from the only reason for the strong immune response in females, Fish said. Hormonal differences and a number of other factors probably play a role, she said.

Researchers have only recently turned their attention to mircoRNAs, and there is likely an incredible amount of information we can learn from them, Fish said.

The paper is published today (Sept. 27) in the journal BioEssays.

Pass it on: Women's seemingly superior immune systems might come from having more microRNAs in their cells than men.

This story was provided by MyHealthNewsDaily, a sister site to LiveScience. Follow MyHealthNewsDaily staff writer Rachael Rettner on Twitter @RachaelRettner. Like us on Facebook.

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Why Women Have Stronger Immune Systems than Men

Four months after federal officials declared manatees are no longer endangered, the U.S. Fish and Wildlife Service has announced that it's now reviewing the endangered status of the Florida panther.

The panther, Florida's state animal, has been on the endangered list since the list was first drawn up in 1967.

Federal rules require the agency to review the status of each endangered or threatened species every five years, and it's time for that routine review, explained Larry Williams, South Florida field supervisor for the Fish and Wildlife Service.

But at least one aspect of the review won't be routine at all.

"One of the most interesting things we're going to review is the taxonomy," Williams said Monday.

Questions have been raised for years about whether the Florida panther is really a distinct sub-species of the pumas found out West, and thus deserving of legal protection.

The questions took a different turn after 1995, when state officials tried an unprecedented experiment to save the panther from inbreeding and genetic defects by bringing in eight female mountain lions from Texas to breed with them.

The cross-breeding saved the panthers, and sparked a baby boom. The panther population, estimated to number no more than 20 to 30 in the mid-1990s, now is estimated at around 200.

But there are Floridians who do not believe the scientists who say the animals now prowling the South Florida wilderness are still Florida panthers. Meanwhile others insist that even if they are, they aren't anything special and probably should be managed by allowing hunting.

In 2000, Williams noted, a team of four scientists led by an expert named Melanie Culver published a paper that said genetics show that all the pumas in North America are one species, period. Because pumas are fairly common, that would mean panthers might no longer be considered endangered.

"Obviously, people who want (endangered species) restrictions lifted have latched onto that," said Elizabeth Fleming of the Defenders of Wildlife Florida office in St. Petersburg.

But she said other experts disagree with the findings of the Culver study. She contended there are physical differences, such as the shape of the skull and the thickness of the fur, that mark the Florida panther as distinct.

The fact that this review is being done by an agency under the Trump Administration, though, makes Fleming concerned.

When it comes to environmental issues, she said, "everything undertaken by the Trump Administration gives me pause."

Williams refused to speculate on whether the five-year review could lead to a decision to change the panthers' status similar to the decision his agency made about manatees. In March, the Fish and Wildlife Service announced it was downgrading manatees from endangered to merely threatened. The controversial move was opposed by most of the people who submitted comments in writing and in public hearings, as well as scientists invited to review it.

As with the manatee, the Fish and Wildlife Service is asking the public for information about panthers. The deadline for submitting comments is Aug. 29.

Last year brought a mix of bad and good news for panthers, which for decades had been largely isolated to habitat south of the Caloosahatchee River near Fort Myers. Occasionally male panthers would cross the river looking for mates that didn't exist. Last year, for the first time ever, biologists spotted females and kittens north of the river, proving the animals were expanding their range.

But last year was also the year that drivers set a record for running over the big cats on the state's highways.

In 2012, a new record for road kills was set with 19. Two years later, in 2014, that record was broken and a new one established at 25 kills. In 2015, that record was shattered when 30 were killed. Then came 2016, with 32 run over on the highways.

The total number of panther deaths, 42 from road kills and other causes, tied 2015.

Panthers, sometimes known among Florida's settlers as "lions" and "catamounts," were a terror of the early frontier for attacks on livestock and pets. By 1981, though, schoolchildren had picked the panther as the state animal choosing it over the alligator, the manatee, the Key deer and a few others that got write-in votes, such as the dolphin and the baboon.

They've proven so popular that the cats have become the mascot for dozens of schools, the namesake of the National Hockey League team in South Florida and a figure on tens of thousands of specialty license plates, sold to cover the costs for the state wildlife commission's panther research.

The wide-ranging predators have lost habitat in South Florida not just to suburban sprawl, but also to the creation of Florida Gulf Coast University and the town of Ave Maria. But Williams said the discovery of breeding cats north of the Caloosahatchee shows they now have much more potential habitat available to them than ever before.

Senior news researcher Caryn Baird contributed to this report. Contact Craig Pittman at craig@tampabay.com. Follow @craigtimes.

Federal officials to review endangered status of Florida panther 07/03/17 [Last modified: Tuesday, July 4, 2017 12:25am] Photo reprints | Article reprints

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Federal officials to review endangered status of Florida panther - Tampabay.com

By Mary Pringle for Island Eye News

A vial containing the DNA sample for Nest #23 on the Isle of Palms which was laid at Summer Dunes Lane on June 16.

You may be aware that this is the 8th nesting season that the Island Turtle Team has taken DNA samples from every nest laid on our islands. This is a huge project involving all of the loggerhead nests in North and South Carolina and Georgia. Recently Dr. Brian Shamblin of the University of Georgia has expanded it to include some of the nests in Florida where many thousands of loggerhead nests are laid each year. It takes multiple years of funding to gather these results.

The purpose of this study is not only to get an accurate picture of the population of nesting loggerheads on the Atlantic Coast but also to find out:

How many clutches of eggs does each nesting female lay in a year?

Is she nesting on more than one beach?

How far apart are her nests?

How many turtles are nesting in more than one state?

Most individual females do not nest every year. How often does each turtle nest: every two years, three years, four or more years?

How precisely does a daughter return to her hatching site to lay her eggs?

Results have shown fascinating things about our nesting females. It takes 25-30 years for a female loggerhead to mature and start laying eggs. This study has shown that there is a grandmother in the Cape Romain National Wildlife Refuge near McClellanville who is still laying nests. She has 14 daughters currently nesting and even has 4 granddaughters nesting! How amazing is that?

In one of the earlier years of the study there was a loggerhead who nested on the Isle of Palms, then two weeks later laid eggs on Hatteras Island in NC, and two weeks after that laid a third nest on Cumberland Island in Georgia. So the information we formerly told people about turtles always returning to the beach where they were hatched is not necessarily true although some of them seem to do so. The study is also showing that individual females usually nest 4 to 6 times in a season at 2 week intervals but then will rest and restore their body condition and skip a year or even two before coming back to lay eggs again. With over 100 eggs each time, this is quite a feat.

We are excited to see the DNA results from the first two nests of 2017. Nest #1 at 56th Avenue, the earliest in NC, SC, or GA, was a faithful IOP nester. She laid eggs here 3 times in 2012. In 2014 she was a busy girl with 4 nests on the IOP and one on Dewees Island.

She did not lay eggs in 2013, 2015 or 2016 but is now back. The mother of our Nest #2, who laid eggs up against the pool fencing at 510 Ocean Blvd, is not as faithful to our island. She nested in 2015, twice in North Carolina and once on Capers Island, but took last season off. It will be interesting to see in our future samples of one eggshell from each of our nests if these two turtles lay more than once on our beaches or where else they go to nest.

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Genetics Research Update - Island Eye News

When a woman breaks up with a man, she usually wants every remnant of him removed from her life. A new study suggests that, try as she might, there may be one last piece of him that shes stuck with for good: his DNA. A study from Australia has managed to prove that fly offspring are able to resemble a mothers previous sexual partner, even when conceived with their fathers sperm.

The idea of telegony, or previous mates influencing a womans offspring, has been around for centuries. It was first proposed by the Greek philosopher Aristotle and was accepted as science until the early 1900s when it was disproved and replaced by more modern genetic theory, according to the study'spress release. Unfortunately, the theory was largely used as a fear tactic to prevent women from copulating with different races or lower classes, but the study suggests the theory may have some elements of truth for flies, at least.

To test the age old theory of telegony, the researchers manipulated male flies to grow to a certain height by changing the amount of nutrients in their diet. They then mated immature females with either large or small males. Later on, the now mature females were again mated with males of various sizes. The subsequent offspring were then studied, and what researchers observed was quite remarkable.

"We found that even though the second male sired the offspring, offspring size was determined by what the mother's previous mating partner ate as a maggot, Dr. Angela Crean, led researcher on the project, explained in the press release. "Our new findings take this to a whole new level showing a male can also transmit some of his acquired features to offspring sired by other males.

The researchers are not yet sure about why this phenomenon occurs but believe it may be due to molecules in the seminal fluid of the first mate being absorbed by the females immature eggs and then influencing the growth of offspring of a later mate. This finding only adds to the already complicated field of genetics. Scientists are only just beginning to grasp the concept that offspring genetics are influenced by non-genetic factors, such as their parents diet. Our new findings take this to a whole new level, Crean said.

To answer the question that Im sure is on every one of your minds, no the researchers are not yet sure whether this phenomenon exists in any other species, but testimony of many experienced breeders suggests it may be.As for humans, I dont even want to begin opening that can of worms, but Crean did tell Medical Daily in an email that she's not ruling out this possibility.

There is no evidence of such effects in humans, but there has not been any research on this possibility in humans. There is a potential for such effects in mammals, explained Crean. For example, there is a lot of foetal DNA in maternal blood during pregnancy, and this could potentially play a role in such effects. There is also evidence in mammals that seminal fluid affects offspring development, so semen from one male could potentially influence the development of eggs fertilized by another male (which is what we think is happening in flies).

Crean added that due to ethical restraints it would be difficult to conduct a similar experiment on humans.

Update: Direct quotes from Dr. Angela Crean have been recently added.

Source: Crean AJ, Kopps AM, Bonduriansky R. Revisiting telegony: offspring inherit an acquired characteristic of mothers previous mate. Ecology. 2014.

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DNA From Sperm Of Ex Partners Lingers In Female Flies And ...

Recording among best weight gains in the first phase of Ekkas Wagyu Challenge, the Hughes familys beef operation appears on-track.

Richard and Dyan Hughes, Wentworth, Clermont introduced Wagyu genetics into their cattle operation 20 years ago and now have Wagyu bulls covering their entire breeding herd.

The Hughes family run more than 10,000 head of cattle across their 40,500 hectare aggregation of properties called Wentworth Station near Clermont, which includes 6000 hectares of sharefarming land, and also run a breeding herd on their Strathalbyn property in Queenslands Burdekin region between Collinsville and Home Hill.

Richard and Dyan Hughes, Wentworth, Clermont placed second in the first phase of this year's Ekka Wagyu Challenge - Best Weight Gain for Pen of Six Grain Fed Wagyu Steers with F2+ Wagyus and achieving a daily average weight gain of 1.23kg.

With a focus on producing highly fertile females and excellent eating quality beef outcomes, the Hughes family have gradually moved towards incorporating more Wagyu genetics in their cattle.

Weve been breeding crossbred Wagyus for at least 20 years and have found we are achieve go results for our beef business with the breed, Mrs Hughes said.

Recently we have started to put Wagyu bulls over our entire breeding herd.

The Hughes started increasing the amount of Wagyu genetics in their herd after noticing very high pregnancy rates in all crossbred Wagyu females at their Burdekin region breeding property.

Any female with some Wagyu in her was falling pregnant very easily, much better than the Brahman/Red Poll-cross females we were running the property, Mrs Hughes said.

It made sense to us to go for fertility when we are also getting the excellent meat eating quality traitswith the Wagyu cattle.

Thats not to say our Brahman cattle didnt have great eating quality as well because weve gone in some taste testing competitions with our Brahman-cross cattle and they can mix it with the best.

Mr Hughes added their cattle operation wanted good fertility traits of the Wagyu breed with the ability of all females to have a calf every year.

The Wagyu breed isvery efficient and fertile type of cattle, he said.

As a cattle operation we have strongly focused on meat quality over the last 15 to 20 years, so I think the beef we produce would be suitable for a dinner table anywhere.

Currently, the Hughes family have a beef supply chain into 400-day Wagyu-cross grain feeding program at Mort and Cos Grassdale feedlot near Dalby, in which Richard and Dyan Hughes are current shareholders in the Mort and Co feedlot.

The season has been very favourable recently for the Hughes familywho previous were in three years of drought across their two large cattle properties.

This is the best our country has looked in many years with good storm rain rolling across our properties since July last year, Mr Hughes said.

We were selling cattle into the live export market and feeder cattle to feedlots during the drought.

We really havent grass finished a steer for four years and this is our first year back at it.

As well as the Wagyu-cross feeder cattle, the Hughes family also run a grass fed beef supply chain that incorporates Red Poll and Brahman genetics originally used in developing a composite bred for their Strathalbyn breeding property in the Burdekin region.

We are now using Wagyu genetics over the Red Poll/Brahman-cross composite cattle as well and selling grass finished steers into a grass fed beef market, Mrs Hughes said.

All we have ever striven for in our cattle operation is fertility and meat quality.

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Hughes benefit from Wagyu fertility and eating quality - Queensland Country Life

In 1977, Alondra Nelson remembers lying stomach-down, head-in-hands, in front of the television, watching Alex Haleys miniseries Roots with her parents. I knew that something special was happening because my parents didnt let us watch TV in the evenings, and here, they were letting us watch eight nights in a row, she told a crowd at the Aspen Ideas Festival, which is co-hosted by the Aspen Institute and The Atlantic. They wanted us to see it for its historic nature.

The miniseries, which traced Haleys genealogy back to the Gambia, spurred many African Americans to start tracing their own ancestries. And it inspired Nelsons own interest in genealogy and the social consequences of learning about ones roots. Now, as the dean of social science at Columbia University, Nelson has spent more than a decade studying what she describes as a new groundswell of root-seekingone propelled by genetic testing.

Today, there are dozens of companies that will sequence segments of a customers DNA and tell them about their ancestry. When Nelson asked the audience how many had made use of such services, at least a dozen people raised their hands. But in 2002, the industry was a nascent one. To find its early customers, Nelson had to go to old-fashioned genealogy clubs and societies.

The history of genetics as a field is steeped in eugenics and scientific racism. And yet, Nelson says that for many African Americans, DNA testing held a special appeal because many of the traditional methods of genealogy had been complicated by the history of slavery. Records disappeared. Names changed. People were trafficked across state lines. Stories were verboten because they were too traumatic. Ancestry testing offered a way of circumventing these obstacles, and airing stories that might never otherwise have come to light. Its an interesting story about race and genetics, Nelson says. When we talk about African Americans in science, its often a story of skepticism and distrust. But this ancestry-testing story is one of pioneering early adopters who are willing to do something different.

One such pioneer was Rick Kittles, a geneticist and cancer researcher who founded a company called African Ancestry Inc. His service provided only broad inferences about where people came from, but for many customers, that was enough. It definitely wasnt perfect, but many people said that if its a choice between no information or an inference that might be slightly off, Ill take the inference, Nelson says.

As tests became more precise, those inferences often proved to be unexpectedly moving. Nelson once met a group of African Americans whose DNA suggested that they had Sierra Leonean ancestry. They met for a ceremony of remembrance on the Ashley River in South Carolina, at a ferry landing where slaves were disembarked from ships and auctioned off. The actor Isaiah Washington was there. A man cast soil and stones from Sierra Leone into the river and said a prayer.

We talk about the history of slavery in this country and it feels so abstract. But genetic ancestry testing can make it very personal, she says. The ceremony allowed for a social practice of healing, where people didnt just have to sit with the knowledge. Many of the folks I talked to tell very moving stories about new relationships they began in their communities with their genetic test results.

Nelson expands on this theme in her recent book, The Social Life of DNA. In it, she argues that DNA is more than a molecule that defines our identity; it also takes a social life beyond its influence within individual bodies. The communities that can arise from ancestry testing are a far cry from the cutesy images often used to sell ancestry tests, in which bemused people swap lederhosen for tartan. This test was not just about identity in a narcissistic way, but about people trying to reconcile the history of slavery, and scaling up from their ancestry test to what it means for the history of the U.S., says Nelson.

When Nelson first looked at ancestry tests, they were mainly of interest to the 50-plus crowd. But theyre now capturing the interest of a younger demographic who are drawn to the quantified-self movement, and the power of dramatically revealing where you came from, reality TV-style. Nelson knows that power first-hand. I didnt want to do the test, but I thought if I was going to do it, it would be with a big reveal, she says.

It happened in an Atlanta ballroom, with Rick Kittles and Isaiah Washington MCing. At the event, Martin Luther King III learned his ancestry on his mothers side traced back to Africa, while his fathers line traced to Scotland and Ireland. He told a story about how were all related in the end, and spoke about his desire to go to Europe. Marcus Garvey Jr.s son heard similar resultsa mothers line that descended from Africa and a fathers line that came from the Iberian Peninsula. He told a story that highlighted the horrors of slavery. It was an example about how these results, even when theyre very similar, get taken up into these stories that are important to us, says Nelson.

She learned that her mitochondrial DNA (which passes down the female line) traced back to the Bamileke people of Cameroona fact that delighted her mother. She couldnt wait to tell everyone, Nelson says. And then soon after, she developed a close relationship with a woman from Cameroon, whose family would spend holidays with us. Her son had grandparents day at school, and since his grandparents are in Cameroon, he invited my motherthe DNA Cameroonianto be his grandparent for the day.

Continue reading here:
How African Americans Use DNA Testing to Connect With Their Past - The Atlantic

Triple X syndrome, also known as trisomy X and 47 XXX, is characterized by the presence of an extra X chromosome in each cell of a female.[1] Those affected are often taller than average. Usually there is no other physical differences and normal fertility. Occasionally there are learning difficulties, decreased muscle tone, seizures, or kidney problems.[1]

Triple X is due to a random event.[1] Triple X can result either during the division of the mother's reproductive cells or during division of cells during early development.[2] It is not typically inherited from one generation to the next. A form where only a percentage of the body cells contain XXX can also occur.[1] Diagnosis is by chromosomal analysis.[3]

Treatment may include speech therapy, physical therapy, and counseling.[3] It occurs in about one in every 1,000 female births.[2] It is estimated that 90% of those affected are not diagnosed as they either have no or only few symptoms.[2] It was first identified in 1959.[4]

Because the vast majority of triple X females are never diagnosed, it may be very difficult to make generalizations about the effects of this syndrome. The samples that were studied were small and may be nonrepresentative. Because of the lyonization, inactivation, and formation of Barr bodies in all female cells, only one X chromosome is active at any time. Thus, triple X syndrome most often has only mild effects or has no effects. The symptoms vary from person to person, with some women being more affected than others.

Symptoms may include tall stature, vertical skin folds that may cover the inner corners of the eyes (epicanthal folds), poor muscle tone, and a curve in the 5th finger towards the 4th.[2] There may also be a small head (microcephaly).[5] There are seldom any observable physical anomalies in triple X females, other than being taller than average.

Poor coordination may be present.[6] Those affected appear to have higher rates of scoliosis.[6]

Epicanthal folds and increased distance between the eyes in 2-year-old girl with trisomy X[2]

The type of finger curvature frequently seen in triple X syndrome

Females with triple X syndrome often have delayed language development.[6] On average those affected have IQs that are 20 points lower.[6] Poor self-esteem, anxiety, and depression are also common.[2][6]

Triple X syndrome is not inherited, but usually, occurs as an event during the formation of reproductive cells (ovum and sperm). An error in cell division called nondisjunction can result in reproductive cells with additional chromosomes. For example, an oocyte or sperm cell may gain an extra copy of the X chromosome as a result of the non-disjunction. If one of these cells contributes to the genetic makeup of a child, the child will have an extra X chromosome in each of her cells. In some cases, trisomy X occurs during cell division in early embryonic development.

Some females with triple X syndrome have an extra X chromosome in only some of their cells. These cases are called 46,XX/47,XXX mosaics.

The vast majority of triple X women are never diagnosed, unless they undergo tests for other medical reasons later in life. Triple X can be diagnosed by a blood test which is able to look at a persons chromosomes (karyotype). Abnormalities on the electroencephalography may be present.[6]

Triple X syndrome can be diagnosed prenatally through amniocentesis or chorionic villus sampling. In Denmark, between 1970 and 1984, 76% of the prenatally diagnosed fetuses with triple-X were aborted. Between 1985-1987, this figure dropped to 56%. With improved information, the number of abortions diminished. In the Netherlands, between 1991 and 2000, 33% (18/54) of the couples that were confronted with a prenatal diagnosis of 47, XXX elected to abort. If balanced information is provided to prospective parents, prenatally, the incidence of voluntary termination (abortion) is reduced.[7]

A stable home environment can improve some of the symptoms.[6]

Triple X syndrome occurs in around 1 in 1,000 girls. On average, five to ten girls with triple X syndrome are born in the United States each day.[8]

The first published report of a woman with a 47,XXX karyotype was by Patricia A. Jacobs, et al. at Western General Hospital in Edinburgh, Scotland, in 1959. It was found in a 35year-old, 5ft. 9 in. (176cm) tall, 128lb. (58.2kg) woman who had premature ovarian failure at age 19; her mother was age 41 and her father was 40 at the time of her conception.[9] Jacobs, et al. called the 47,XXX woman a "superfemale", a term which was immediately criticized, did not gain acceptance, and was based on the incorrect assumption that the sex-determination system in mammals was the same as in the fruit fly Drosophila.[10] British pathologist and geneticist Bernard Lennox, the principal consultant on medical terms for the Oxford English Dictionary, suggested the term "XXX syndrome".[11]

Read more here:
Triple X syndrome - Wikipedia

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects (Drosophila), and some plants (Ginkgo). In this system, the sex of an individual is determined by a pair of sex chromosomes (gonosomes). Females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex.

This system is in contrast with the ZW sex-determination system found in birds, some insects, many reptiles, and other animals, in which the heterogametic sex is female.

A temperature-dependent sex determination system is found in some reptiles.

All animals have a set of DNA coding for genes present on chromosomes. In humans, most mammals, and some other species, two of the chromosomes, called the X chromosome and Y chromosome, code for sex. In these species, one or more genes are present on their Y-chromosome that determine maleness. In this process, an X chromosome and a Y chromosome act to determine the sex of offspring, often due to genes located on the Y chromosome that code for maleness. Offspring have two sex chromosomes: an offspring with two X chromosomes will develop female characteristics, and an offspring with an X and a Y chromosome will develop male characteristics.

In humans, half of spermatozoons carry X chromosome and the other half Y chromosome.[1] A single gene (SRY) present on the Y chromosome acts as a signal to set the developmental pathway towards maleness. Presence of this gene starts off the process of virilization. This and other factors result in the sex differences in humans.[2] The cells in females, with two X chromosomes, undergo X-inactivation, in which one of the two X chromosomes is inactivated. The inactivated X chromosome remains within a cell as a Barr body.

Humans, as well as some other organisms, can have a chromosomal arrangement that is contrary to their phenotypic sex; for example, XX males or XY females (see androgen insensitivity syndrome). Additionally, an abnormal number of sex chromosomes (aneuploidy) may be present, such as Turner's syndrome, in which a single X chromosome is present, and Klinefelter's syndrome, in which two X chromosomes and a Y chromosome are present, XYY syndrome and XXYY syndrome.[2] Other less common chromosomal arrangements include: triple X syndrome, 48, XXXX, and 49, XXXXX.

In most mammals, sex is determined by presence of Y. "Female" is the default sex; due to the absence of the Y.[3] In the 1930s, Alfred Jost determined that the presence of testosterone was required for Wolffian duct development in the male rabbit.[4]

SRY is a sex-determining gene on the Y chromosome in the therians (placental mammals and marsupials).[5] Non-human mammals use several genes on the Y-chromosome. Not all male-specific genes are located on the Y-chromosome. Other species (including most Drosophila species) use the presence of two X chromosomes to determine femaleness. One X chromosome gives putative maleness. The presence of Y-chromosome genes is required for normal male development.

Birds and many insects have a similar system of sex determination (ZW sex-determination system), in which it is the females that are heterogametic (ZW), while males are homogametic (ZZ).

Many insects of the order Hymenoptera instead have a system (the haplo-diploid sex-determination system), where the males are haploid individuals (which have just one chromosome of each type), while the females are diploid (with chromosomes appearing in pairs). Some other insects have the X0 sex-determination system, where just one chromosome type appears in pairs for the female but alone in the males, while all other chromosomes appear in pairs in both sexes.[citation needed]

For a long time, biologists believed that the female form was the default template for the mammalian fetuses of both sexes. After the discovery of the testis-determining gene SRY, many scientists shifted to the theory that the genetic mechanism that determines a fetus to develop into a male form was initiated by the SRY gene, which was thought to be responsible for the production of testosterone and its overall effects on body and brain development. This perspective still shared the classical way of thinking; that in order to produce two sexes, nature has developed a default female pathway and an active pathway by which male genes would initiate the process of determining a male sex, as something that is developed in addition to and based on the default female form. This view is no longer considered accurate by most scientists who study the genetics of sex. In an interview for the Rediscovering Biology website,[6] researcher Eric Vilain described how the paradigm changed since the discovery of the SRY gene:

For a long time we thought that SRY would activate a cascade of male genes. It turns out that the sex determination pathway is probably more complicated and SRY may in fact inhibit some anti-male genes.

The idea is instead of having a simplistic mechanism by which you have pro-male genes going all the way to make a male, in fact there is a solid balance between pro-male genes and anti-male genes and if there is a little too much of anti-male genes, there may be a female born and if there is a little too much of pro-male genes then there will be a male born.

We [are] entering this new era in molecular biology of sex determination where it's a more subtle dosage of genes, some pro-males, some pro-females, some anti-males, some anti-females that all interplay with each other rather than a simple linear pathway of genes going one after the other, which makes it very fascinating but very complicated to study.

In mammals, including humans, the SRY gene is responsible with triggering the development of non-differentiated gonads into testes, rather than ovaries. However, there are cases in which testes can develop in the absence of an SRY gene (see sex reversal). In these cases, the SOX9 gene, involved in the development of testes, can induce their development without the aid of SRY. In the absence of SRY and SOX9, no testes can develop and the path is clear for the development of ovaries. Even so, the absence of the SRY gene or the silencing of the SOX9 gene are not enough to trigger sexual differentiation of a fetus in the female direction. A recent finding indicates that ovary development and maintenance is an active process,[7] regulated by the expression of a "pro-female" gene, FOXL2. In an interview[8] for the TimesOnline edition, study co-author Robin Lovell-Badge explained the significance of the discovery:

We take it for granted that we maintain the sex we are born with, including whether we have testes or ovaries. But this work shows that the activity of a single gene, FOXL2, is all that prevents adult ovary cells turning into cells found in testes.

Looking into the genetic determinants of human sex can have wide-ranging consequences. Scientists have been studying different sex determination systems in fruit flies and animal models to attempt an understanding of how the genetics of sexual differentiation can influence biological processes like reproduction, ageing[9] and disease.

In humans and many other species of animals, the father determines the sex of the child. In the XY sex-determination system, the female-provided ovum contributes an X chromosome and the male-provided sperm contributes either an X chromosome or a Y chromosome, resulting in female (XX) or male (XY) offspring, respectively.

Hormone levels in the male parent affect the sex ratio of sperm in humans.[10] Maternal influences also impact which sperm are more likely to achieve conception.

Human ova, like those of other mammals, are covered with a thick translucent layer called the zona pellucida, which the sperm must penetrate to fertilize the egg. Once viewed simply as an impediment to fertilization, recent research indicates the zona pellucida may instead function as a sophisticated biological security system that chemically controls the entry of the sperm into the egg and protects the fertilized egg from additional sperm.[11]

Recent research indicates that human ova may produce a chemical which appears to attract sperm and influence their swimming motion. However, not all sperm are positively impacted; some appear to remain uninfluenced and some actually move away from the egg.[12]

Maternal influences may also be possible that affect sex determination in such a way as to produce fraternal twins equally weighted between one male and one female.[13]

The time at which insemination occurs during the oestrus cycle has been found to affect the sex ratio of the offspring of humans, cattle, hamsters, and other mammals.[10] Hormonal and pH conditions within the female reproductive tract vary with time, and this affects the sex ratio of the sperm that reach the egg.[10]

Sex-specific mortality of embryos also occurs.[10]

Since ancient times, people have believed that the sex of an infant is determined by how much heat a man's sperm had during insemination. Aristotle wrote that:

...the semen of the male differs from the corresponding secretion of the female in that it contains a principle within itself of such a kind as to set up movements also in the embryo and to concoct thoroughly the ultimate nourishment, whereas the secretion of the female contains material alone. If, then, the male element prevails it draws the female element into itself, but if it is prevailed over it changes into the opposite or is destroyed.

Aristotle claimed that the male principle was the driver behind sex determination,[14] such that if the male principle was insufficiently expressed during reproduction, the fetus would develop as a female.

Nettie Stevens and Edmund Beecher Wilson are credited with independently discovering, in 1905, the chromosomal XY sex-determination system, i.e. the fact that males have XY sex chromosomes and females have XX sex chromosomes.[15][16][17]

The first clues to the existence of a factor that determines the development of testis in mammals came from experiments carried out by Alfred Jost,[18] who castrated embryonic rabbits in utero and noticed that they all developed as female.[citation needed]

In 1959, C. E. Ford and his team, in the wake of Jost's experiments, discovered[19] that the Y chromosome was needed for a fetus to develop as male when they examined patients with Turner's syndrome, who grew up as phenotypic females, and found them to be X0 (hemizygous for X and no Y). At the same time, Jacob & Strong described a case of a patient with Klinefelter syndrome (XXY),[20] which implicated the presence of a Y chromosome in development of maleness.[21]

All these observations lead to a consensus that a dominant gene that determines testis development (TDF) must exist on the human Y chromosome.[21] The search for this testis-determining factor (TDF) led a team of scientists[22] in 1990 to discover a region of the Y chromosome that is necessary for the male sex determination, which was named SRY (sex-determining region of the Y chromosome).[21]

Read more:
XY sex-determination system - Wikipedia

Venus de Milo at the Louvre has been described as a "classical vision of beauty".[1][2][3] However, one expert claimed her "almost matronly representation" was meant to convey an "impressive appearance" rather than "ideal female beauty".[4]

Physical attractiveness is the degree to which a person's physical features are considered aesthetically pleasing or beautiful. The term often implies sexual attractiveness or desirability, but can also be distinct from either. There are many factors which influence one person's attraction to another, with physical aspects being one of them. Physical attraction itself includes universal perceptions common to all human cultures, as well as aspects that are culturally and socially dependent, along with individual subjective preferences.

In many cases, humans subconsciously attribute positive characteristics, such as intelligence and honesty, to physically attractive people.[9] From research done in the United States and United Kingdom, it was found that the association between intelligence and physical attractiveness is stronger among men than among women.[10]Evolutionary psychologists have tried to answer why individuals who are more physically attractive should also, on average, be more intelligent, and have put forward the notion that both general intelligence and physical attractiveness may be indicators of underlying genetic fitness.[11] A person's physical characteristics can signal cues to fertility and health. Attending to these factors increases reproductive success, furthering the representation of one's genes in the population.[12]

Men, on average, tend to be attracted to women who are shorter than they are, have a youthful appearance, and exhibit features such as a symmetrical face,[13] full breasts, full lips, and a low waist-hip ratio.[14] Women, on average, tend to be attracted to men who are taller than they are, display a high degree of facial symmetry, masculine facial dimorphism, and who have broad shoulders, a relatively narrow waist, and a V-shaped torso.[15][16]

Generally, physical attractiveness can be viewed from a number of perspectives; with universal perceptions being common to all human cultures, cultural and social aspects, and individual subjective preferences. The perception of attractiveness can have a significant effect on how people are judged in terms of employment or social opportunities, friendship, sexual behavior, and marriage.[17]

Some physical features are attractive in both men and women, particularly bodily[18] and facial symmetry,[19][20][21][22] although one contrary report suggests that "absolute flawlessness" with perfect symmetry can be "disturbing".[23] Symmetry may be evolutionarily beneficial as a sign of health because asymmetry "signals past illness or injury".[24] One study suggested people were able to "gauge beauty at a subliminal level" by seeing only a glimpse of a picture for one-hundredth of a second.[24] Other important factors include youthfulness, skin clarity and smoothness of skin; and "vivid color" in the eyes and hair.[19] However, there are numerous differences based on gender.

A 1921 study, of the reports of college students regarding those traits in individuals which make for attractiveness and repulsiveness argued that static traits, such as beauty or ugliness of features, hold a position subordinate to groups of physical elements like expressive behavior, affectionate disposition, grace of manner, aristocratic bearing, social accomplishments, and personal habits.[25]

Grammer and colleagues have identified eight "pillars" of beauty: youthfulness, symmetry, averageness, sex-hormone markers, body odor, motion, skin complexion and hair texture.[26]

Most studies of the brain activations associated with the perception of attractiveness show photographs of faces to their participants and let them or a comparable group of people rate the attractiveness of these faces. Such studies consistently find that activity in certain parts of the orbitofrontal cortex increases with increasing attractiveness of faces.[27][28][29][30][31] This neural response has been interpreted as a reaction on the rewarding nature of attractiveness, as similar increases in activation in the medial orbitofrontal cortex can be seen in response to smiling faces[32] and to statements of morally good actions.[29][31] While most of these studies have not assessed participants of both genders or homosexual individuals, evidence from one study including male and female hetero- and homosexual individuals indicate that some of the aforementioned increases in brain activity are restricted to images of faces of the gender participants feel sexually attracted to.[33]

With regard to brain activation related to the perception of attractive bodies, one study with heterosexual participants suggests that activity in the nucleus accumbens and the anterior cingulate cortex increases with increasing attractiveness. The same study finds that for faces and bodies alike, the medial part of the orbitofrontal cortex responds with greater activity to both very attractive and very unattractive pictures.[34]

Women, on average, tend to be more attracted to men who have a relatively narrow waist, a V-shaped torso, and broad shoulders. Women also tend to be more attracted to men who are taller than they are, and display a high degree of facial symmetry, as well as relatively masculine facial dimorphism.[15][16] With regard to male-male-attractiveness, one source reports that the most important factor that attracts gay men to other males is the man's physical attractiveness.[35]

Studies have shown that ovulating heterosexual women prefer faces with masculine traits associated with increased exposure to testosterone during key developmental stages, such as a broad forehead, relatively longer lower face, prominent chin and brow, chiseled jaw and defined cheekbones.[36] The degree of differences between male and female anatomical traits is called sexual dimorphism. Female respondents in the follicular phase of their menstrual cycle were significantly more likely to choose a masculine face than those in menses and luteal phases,[37] (or in those taking hormonal contraception).[15][16][38][39] This distinction supports the sexy son hypothesis, which posits that it is evolutionarily advantageous for women to select potential fathers who are more genetically attractive,[40] rather than the best caregivers.[41] However, women's likeliness to exert effort to view male faces does not seem to depend on their masculinity, but to a general increase with women's testosterone levels.[42]

It is suggested that the masculinity of facial features is a reliable indication of good health, or, alternatively, that masculine-looking males are more likely to achieve high status.[43] However, the correlation between attractive facial features and health has been questioned.[44] Sociocultural factors, such as self-perceived attractiveness, status in a relationship and degree of gender-conformity, have been reported to play a role in female preferences for male faces.[45] Studies have found that women who perceive themselves as physically attractive are more likely to choose men with masculine facial dimorphism, than are women who perceive themselves as physically unattractive.[46] In men, facial masculinity significantly correlates with facial symmetryit has been suggested that both are signals of developmental stability and genetic health.[47] One study called into question the importance of facial masculinity in physical attractiveness in men arguing that when perceived health, which is factored into facial masculinity, is discounted it makes little difference in physical attractiveness.[48] In a cross-country study involving 4,794 women in their early twenties, a difference was found in women's average "masculinity preference" between countries.[49]

A study found that the same genetic factors cause facial masculinity in both males and females such that a male with a more masculine face would likely have a sister with a more masculine face due to the siblings having shared genes. The study also found that, although female faces that were more feminine were judged to be more attractive, there was no association between male facial masculinity and male facial attractiveness for female judges. With these findings, the study reasoned that if a woman were to reproduce with a man with a more masculine face, then her daughters would also inherit a more masculine face, making the daughters less attractive. The study concluded that there must be other factors that advantage the genetics for masculine male faces to offset their reproductive disadvantage in terms of "health", "fertility" and "facial attractiveness" when the same genetics are present in females. The study reasoned that the "selective advantage" for masculine male faces must "have (or had)" been due to some factor that is not directly tied to female perceptions of male facial attractiveness.[50]

In a study of 447 gay men in China, researchers said that tops preferred feminized male faces, bottoms preferred masculinized male faces and versatiles had no preference for either feminized or masculinized male faces.[51]

In pre-modern Chinese literature, the ideal man in caizi jiaren romances was said to have "rosy lips, sparkling white teeth" and a "jasper-like face" (Chinese: ).[52][53]

In Middle English literature, a beautiful man should have a long, broad and strong face.[54]

A study that used Chinese, Malay and Indian judges said that Chinese men with orthognathism where the mouth is flat and in-line with the rest of the face were judged to be the most attractive and Chinese men with a protruding mandible where the jaw projects outward were judged to be the least attractive.[55]

Symmetrical faces and bodies may be signs of good inheritance to women of child-bearing age seeking to create healthy offspring. Studies suggest women are less attracted to men with asymmetrical faces,[56] and symmetrical faces correlate with long term mental performance[57] and are an indication that a man has experienced "fewer genetic and environmental disturbances such as diseases, toxins, malnutrition or genetic mutations" while growing.[57] Since achieving symmetry is a difficult task during human growth, requiring billions of cell reproductions while maintaining a parallel structure, achieving symmetry is a visible signal of genetic health.

Studies have also suggested that women at peak fertility were more likely to fantasize about men with greater facial symmetry,[58] and other studies have found that male symmetry was the only factor that could significantly predict the likelihood of a woman experiencing orgasm during sex. Women with partners possessing greater symmetry reported significantly more copulatory female orgasms than were reported by women with partners possessing low symmetry, even with many potential confounding variables controlled.[59] This finding has been found to hold across different cultures. It has been argued that masculine facial dimorphism (in men) and symmetry in faces are signals advertising genetic quality in potential mates.[60] Low facial and body fluctuating asymmetry may indicate good health and intelligence, which are desirable features.[61] Studies have found that women who perceive themselves as being more physically attractive are more likely to favor men with a higher degree of facial symmetry, than are women who perceive themselves as being less physically attractive.[46] It has been found that symmetrical men (and women) have a tendency to begin to have sexual intercourse at an earlier age, to have more sexual partners, and to have more one-night stands. They are also more likely to be prone to infidelity.[62] A study of quarterbacks in the American National Football League found a positive correlation between facial symmetry and salaries.[20]

Double-blind studies found that women prefer the scent of men who are rated as facially attractive.[63] For example, both males and females were more attracted to the natural scent of individuals who had been rated by consensus as facially attractive.[64] Additionally, it has also been shown that women have a preference for the scent of men with more symmetrical faces, and that women's preference for the scent of more symmetrical men is strongest during the most fertile period of their menstrual cycle.[65] Within the set of normally cycling women, individual women's preference for the scent of men with high facial symmetry correlated with their probability of conception.[65]

Studies have explored the genetic basis behind such issues as facial symmetry and body scent and how they influence physical attraction. In one study in which women wore men's T-shirts, researchers found that women were more attracted to the bodily scents in shirts of men who had a different type of gene section within the DNA called Major histocompatibility complex (MHC).[66] MHC is a large gene area within the DNA of vertebrates which encodes proteins dealing with the immune system[67] and which influences individual bodily odors.[68] One hypothesis is that humans are naturally attracted by the sense of smell and taste to others with dissimilar MHC sections, perhaps to avoid subsequent inbreeding while increasing the genetic diversity of offspring.[67] Further, there are studies showing that women's natural attraction for men with dissimilar immune profiles can be distorted with use of birth control pills.[68] Other research findings involving the genetic foundations of attraction suggest that MHC heterozygosity positively correlates with male facial attractiveness. Women judge the faces of men who are heterozygous at all three MHC loci to be more attractive than the faces of men who are homozygous at one or more of these loci. Additionally, a second experiment with genotyped women raters, found these preferences were independent of the degree of MHC similarity between the men and the female rater. With MHC heterozygosity independently seen as a genetic advantage, the results suggest that facial attractiveness in men may be a measure of genetic quality.[69][70]

A 2010 OkCupid study on 200,000 of its male and female dating site users found that women are, except those during their early to mid-twenties, open to relationships with both somewhat older and somewhat younger men; they have a larger potential dating pool than men until age 26. At age 20, women, in a "dramatic change", begin sending private messages to significantly older men. At age 29 they become "even more open to older men". Male desirability to women peaks in the late 20s and does not fall below the average for all men until 36.[71] Other research indicates that women, irrespective of their own age, are attracted to men who are the same age or older.[72]

For the Romans especially, "beardlessness" and "smooth young bodies" were considered beautiful to both men and women.[73] For Greek and Roman men, the most desirable traits of boys were their "youth" and "hairlessness". Pubescent boys were considered a socially appropriate object of male desire, while post-pubescent boys were considered to be "" or "past the prime".[73] This was largely in the context of pederasty (adult male interest in adolescent boys). Today, men and women's attitudes towards male beauty has changed. For example, body hair on men may even be preferred (see below).

A 1984 study said that gay men tend to prefer gay men of the same age as ideal partners, but there was a statistically significant effect (p < 0.05) of masculinity-femininity. The study said that more feminine men tended to prefer relatively older men than themselves and more masculine men tended to prefer relatively younger men than themselves.[74]

The physique of a slim waist, broad shoulders and muscular chest are often found to be attractive to females.[75] Further research has shown that, when choosing a mate, the traits females look for indicate higher social status, such as dominance, resources, and protection.[76] An indicator of health in males (a contributing factor to physical attractiveness) is the android fat distribution pattern which is categorized as more fat distributed on the upper body and abdomen, commonly referred to as the "V shape."[76] When asked to rate other men, both heterosexual and homosexual men found low waist-to-chest ratios (WCR) to be more attractive on other men, with the gay men showing a preference for lower WCR (more V-shaped) than the straight men.[77]

Other researchers found waist-to-chest ratio the largest determinant of male attractiveness, with body mass index and waist-to-hip ratio not as significant.[78]

Women focus primarily on the ratio waist to chest or more specifically waist to shoulder. This is analogous to the waist to hip ratio (WHR) that men prefer. Key body image for a man in the eyes of a woman would include big shoulders, chest, and upper back, and a slim waist area.[79] Research has additionally shown that college males had a better satisfaction with their body than college females. The research also found that when a college female's waist to hip ratio went up, their body image satisfaction decreased.[80] The results indicate that males had significantly greater body image satisfaction than did females.

Some research has shown that body weight may have a stronger effect than WHR when it comes to perceiving attractiveness of the opposite sex. It was found that waist to hip ratio played a smaller role in body preference than body weight in regards to both sexes.[81]

Psychologists Viren Swami and Martin J. Tovee compared female preference for male attractiveness cross culturally, between Britain and Malaysia. They found that females placed more importance on WCR (and therefore body shape) in urban areas of Britain and Malaysia, while females in rural areas placed more importance on BMI (therefore weight and body size). Both WCR and BMI are indicative of male status and ability to provide for offspring, as noted by evolutionary theory.[82]

Females have been found to desire males that are normal weight and have the average WHR for a male. Females view these males as attractive and healthy. Males who had the average WHR but were overweight or underweight are not perceived as attractive to females. This suggests that WHR is not a major factor in male attractiveness, but a combination of body weight and a typical male WHR seem to be the most attractive. Research has shown that men who have a higher waist to hip ratio and a higher salary are perceived as more attractive to women.[83]

A 1982 study, found that an abdomen that protrudes was the "least attractive" trait for men.[84]

In Middle English literature, a beautiful man should have a flat abdomen.[54]

Men's bodies portrayed in magazines marketed to men are more muscular than the men's bodies portrayed in magazines marketed to women. From this, some have concluded that men perceive a more muscular male body to be ideal, as distinct from a woman's ideal male, which is less muscular than what men perceive to be ideal.[85] This is due to the within-gender prestige granted by increased muscularity and within-gender competition for increased muscularity.[85] Men perceive the attractiveness of their own musculature by how closely their bodies resemble the "muscle man."[86] This "muscle man" ideal is characterized by large muscular arms, especially biceps, a large muscular chest that tapers to their waist and broad shoulders.[86]

In a study of stated profile preferences on Match.com, a greater percentage of gay men than lesbians selected their ideal partner's body type as "Athletic and Toned" as opposed to the other two options of "Average" or "Overweight".[87]

In pre-modern Chinese literature, such as in The Story of the Western Wing, a type of masculinity called "scholar masculinity" is depicted wherein the "ideal male lover" is "weak, vulnerable, feminine, and pedantic".[52]

In Middle English literature, a beautiful man should have thick, broad shoulders, a square and muscular chest, a muscular back, strong sides that taper to a small waist, large hands and arms and legs with huge muscles.[54]

A 2006 study, of 25,594 heterosexual men found that men who perceived themselves as having a large penis were more satisfied with their own appearance.[88]

A 2014 study, criticized previous studies based on the fact that they relied on images and used terms such as "small", "medium", and "large" when asking for female preference. The new study used 3D models of penises from sizes of 4 inches (10cm) long and 2.5 inches (6.4cm) in circumference to 8.5 inches (22cm) long and 7 inches (18cm) in circumference and let the women "view and handle" them. It was found that women overestimated the actual size of the penises they have experimented with when asked in a follow-up survey. The study concluded that women on average preferred the 6.5-inch (17cm) penis in length both for long-term and for one-time partners. Penises with larger girth were preferred for one-time partners.[89]

Females' sexual attraction towards males may be determined by the height of the man.[91] Height in men is associated with status or wealth in many cultures (in particular those where malnutrition is common),[92] which is beneficial to women romantically involved with them. One study conducted of women's personal ads support the existence of this preference; the study found that in ads requesting height in a mate, 80% requested a height of 6 feet (1.83m) or taller.[92] The online dating Website eHarmony only matches women with taller men because of complaints from women matched with shorter men.[93]

Other studies have shown that heterosexual women often prefer men taller than they are rather than a man with above average height. While women usually desire men to be at least the same height as themselves or taller, several other factors also determine male attractiveness, and the male-taller norm is not universal.[94] For example, taller women are more likely to relax the "taller male" norm than shorter women.[95] Furthermore, professor Adam Eyre-Walker, from the University of Sussex, has stated that there is, as of yet, no evidence that these preferences are evolutionary preferences, as opposed to merely cultural preferences.[96] In a double-blind study by Graziano et al., it was found that, in person, using a sample of women of normal size, they were on average most attracted to men who were of medium height (5'9" 5'11", 1.75m 1.80m) and less attracted to both men of shorter height (5'5" 5'7", 1.65m 1.70m) and men of tallest height (6'2" 6'4", 1.88m 1.93m).[97]

Additionally, women seem more receptive to an erect posture than men, though both prefer it as an element within beauty.[92] According to one study (Yee N., 2002), gay men who identify as "only tops" tend to prefer shorter men, while gay men who identify as "only bottoms" tend to prefer taller men.[98]

In romances in Middle English literature, all of the "ideal" male heroes are tall, and the vast majority of the "valiant" male heroes are tall too.[54]

Studies based in the United States, New Zealand, and China have shown that women rate men with no trunk (chest and abdominal) hair as most attractive, and that attractiveness ratings decline as hairiness increases.[99][100] Another study, however, found that moderate amounts of trunk hair on men was most attractive, to the sample of British and Sri Lankan women.[101] Further, a degree of hirsuteness (hairiness) and a waist-to-shoulder ratio of 0.6 is often preferred when combined with a muscular physique.[101]

In a study using Finnish women, women with hairy fathers were more likely to prefer hairy men, suggesting that preference for hairy men is the result of either genetics or imprinting.[102] Among gay men, another study (Yee N., 2002) reported gay males who identify as "only tops" prefer less hairy men, while gay males who identify as "only bottoms" prefer hairier men.[98]

Testosterone has been shown to darken skin color in laboratory experiments.[103] In his foreword to Peter Frost's 2005 Fair Women, Dark Men, University of Washington sociologist Pierre L. van den Berghe writes: "Although virtually all cultures express a marked preference for fair female skin, even those with little or no exposure to European imperialism, and even those whose members are heavily pigmented, many are indifferent to male pigmentation or even prefer men to be darker."[104] Despite this, the aesthetics of skin tone varies from culture to culture. Manual laborers who spent extended periods of time outside developed a darker skin tone due to exposure to the sun. As a consequence, an association between dark skin and the lower classes developed. Light skin became an aesthetic ideal because it symbolized wealth. "Over time society attached various meanings to these colored differences. Including assumptions about a person's race, socioeconomic class, intelligence, and physical attractiveness."[105]

A scientific review published in 2011, identified from a vast body of empirical research that skin colour as well as skin tone tend to be preferred as they act as indicators of good health. More specifically, these indicators are thought to suggest to potential mates that the beholder has strong or good genes capable of fighting off disease.[106]

According to one study (Yee N., 2002), gay men who identify as "only tops" tend to prefer lighter-skinned men while gay men who identify as "only bottoms" tend to prefer darker-skinned men.[98]

More recent research has suggested that redder and yellower skin tones,[107] reflecting higher levels of oxygenated blood,[108] carotenoid and to a lesser extent melanin pigment, and net dietary intakes of fruit and vegetables,[109] appears healthier, and therefore more attractive.[110]

Research indicates that heterosexual men tend to be attracted to young[111] and beautiful women[112] with bodily symmetry.[113] Rather than decreasing it, modernity has only increased the emphasis men place on women's looks.[114]Evolutionary psychologists attribute such attraction to an evaluation of the fertility potential in a prospective mate.[111]

Research has attempted to determine which facial features communicate attractiveness. Facial symmetry has been shown to be considered attractive in women,[117][118] and men have been found to prefer full lips,[119] high forehead, broad face, small chin, small nose, short and narrow jaw, high cheekbones,[56][120] clear and smooth skin, and wide-set eyes.[111] The shape of the face in terms of "how everything hangs together" is an important determinant of beauty.[121] A University of Toronto study found correlations between facial measurements and attractiveness; researchers varied the distance between eyes, and between eyes and mouth, in different drawings of the same female face, and had the drawings evaluated; they found there were ideal proportions perceived as attractive (see photo).[115] These proportions (46% and 36%) were close to the average of all female profiles.[115] Women with thick, dark limbal rings in their eyes have also been found to be more attractive. The explanation given is that because the ring tends to fade with age and medical problems, a prominent limbal ring gives an honest indicator of youth.[122]

In a cross-cultural study, more neotenized (i.e., youthful looking) female faces were found to be most attractive to men while less neotenized female faces were found to be less attractive to men, regardless of the females' actual age.[123] One of these desired traits was a small jaw.[124] In a study of Italian women who have won beauty competitions, it was found that their faces had more "babyish" (pedomorphic) traits than those of the "normal" women used as a reference.[125]

In a cross-cultural study, Marcinkowska et al. said that 18- to 45-year-old heterosexual men in all 28 countries surveyed preferred photographs of 18- to 24-year-old Caucasian women whose faces were feminized using Psychomorph software over faces of 18- to 24-year-old Caucasian women that were masculinized using that software, but there were differences in preferences for femininity across countries. The higher the National Health Index of a country, the more were the feminized faces preferred over the masculinized faces. Among the countries surveyed, Japan had the highest femininity preference and Nepal had the lowest femininity preference.[128]

Michael R. Cunningham of the Department of Psychology at the University of Louisville found, using a panel of East Asian, Hispanic and White judges, that the Asian, Hispanic and White female faces found most attractive were those that had "neonate large eyes, greater distance between eyes, and small noses"[129] and his study led him to conclude that "large eyes" were the most "effective" of the "neonate cues".[129] Cunningham also said that "shiny" hair may be indicative of "neonate vitality".[129] Using a panel of blacks and whites as judges, Cunningham found more neotenous faces were perceived as having both higher "femininity" and "sociability".[129] In contrast, Cunningham found that faces that were "low in neoteny" were judged as "intimidating".[129] Cunningham noted a "difference" in the preferences of Asian and white judges with Asian judges preferring women with "less mature faces" and smaller mouths than the White judges.[129] Cunningham hypothesized that this difference in preference may stem from "ethnocentrism" since "Asian faces possess those qualities", so Cunningham re-analyzed the data with "11 Asian targets excluded" and concluded that "ethnocentrism was not a primary determinant of Asian preferences."[129] Rather than finding evidence for purely "neonate" faces being most appealing, Cunningham found faces with "sexually-mature" features at the "periphery" of the face combined with "neonate" features in the "center of the face" most appealing in men and women.[129] Upon analyzing the results of his study, Cunningham concluded that preference for "neonate features may display the least cross-cultural variability" in terms of "attractiveness ratings"[129] and, in another study, Cunningham concluded that there exists a large agreement on the characteristics of an attractive face.[130][131]

In computer face averaging tests, women with averaged faces have been shown to be considered more attractive.[22][132] This is possibly due to average features being more familiar and, therefore, more comfortable.[117]

Commenting on the prevalence of whiteness in supposed beauty ideals in his book White Lies: Race and the Myth of Whiteness, Maurice Berger states that the schematic rendering in the idealized face of a study conducted with American subjects had "straight hair," "light skin," "almond-shaped eyes," "thin, arched eyebrows," "a long, thin nose, closely set and tiny nostrils" and "a large mouth and thin lips",[133] though the author of the study stated that there was consistency between his results and those conducted on other races. Scholar Liu Jieyu says in the article White Collar Beauties, "The criterion of beauty is both arbitrary and gendered. The implicit consensus is that women who have fair skin and a slim figure with symmetrical facial features are pretty." He says that all of these requirements are socially constructed and force people to change themselves to fit these criteria.[134]

One psychologist speculated there were two opposing principles of female beauty: prettiness and rarity. So on average, symmetrical features are one ideal, while unusual, stand-out features are another.[135] A study performed by the University of Toronto found that the most attractive facial dimensions were those found in the average female face. However, that particular University of Toronto study looked only at white women.[136]

A study that used Chinese, Malay and Indian judges said that Chinese women with orthognathism where the mouth is flat and in-line with the rest of the face were judged to be the most attractive and Chinese women with a protruding mandible where the jaw projects outward were judged to be the least attractive.[55]

A 2011 study, by Wilkins, Chan and Kaiser found correlations between perceived femininity and attractiveness, that is, women's faces which were seen as more feminine were judged by both men and women to be more attractive.[137]

A component of the female beauty ideal in Persian literature is for women to have faces like a full moon.[138][139][140]

In Arabian society in the Middle Ages, a component of the female beauty ideal was for women to have round faces which were like a "full moon".[141]

In Japan, during the Edo period, a component of the female beauty ideal was for women to have long and narrow faces which were shaped like ovals.[142]

In Jewish Rabbinic literature, the Rabbis considered full lips to be the ideal type of lips for women.[143]

Historically, in Chinese and Japanese literature, the feminine ideal was said to include small lips.[144] Women would paint their lips thinner and narrower to align with this ideal.[145][146]

Classical Persian literature, paintings, and miniatures portrayed traits such as long black curly hair, a small mouth, long arched eyebrows, large almond shaped eyes, a small nose, and beauty spots as being beautiful for women.[147]

Evidence from various cultures suggests that heterosexual men tend to find the sight of women's genitalia to be sexually arousing.[148]

Cross-cultural data shows that the reproductive success of women is tied to their youth and physical attractiveness[149] such as the pre-industrial Sami where the most reproductively successful women were 15 years younger than their man.[150] One study covering 37 cultures showed that, on average, a woman was 2.5 years younger than her male partner, with the age difference in Nigeria and Zambia being at the far extreme of 6.5 to 7.5 years. As men age, they tend to seek a mate who is ever younger.[111]

25% of eHarmony's male customers over the age of 50 request to only be matched with women younger than 40.[93] A 2010 OkCupid study, of 200,000 users found that female desirability to its male users peaks at age 21, and falls below the average for all women at 31. After age 26, men have a larger potential dating pool than women on the site; and by age 48, their pool is almost twice as large. The median 31-year-old male user searches for women aged 22 to 35, while the median 42-year-old male searches for women 27 to 45. The age skew is even greater with messages to other users; the median 30-year-old male messages teenage girls as often as women his own age, while mostly ignoring women a few years older than him. Excluding the 10% most and 10% least beautiful of women, however, women's attractiveness does not change between 18 and 40, but if extremes are not excluded "There's no doubt that younger [women] are more physically attractiveindeed in many ways beauty and youth are inextricable. That's why most of the models you see in magazines are teenagers".[71]

Pheromones (detected by female hormone markers) reflects female fertility and the reproductive value mean.[151] As females age, the estrogen-to-androgen production ratio changes and results in female faces to appear more and more masculine (thus appearing less "attractive").[151] In a small (n=148) study performed in the United States, using male college students at one university, the mean age expressed as ideal for a wife was found to be 16.87 years old, while 17.76 was the mean ideal age for a brief sexual encounter. However, the study sets up a framework where "taboos against sex with young girls" are purposely diminished, and biased their sample by removing any participant over the age of 30, with a mean participant age of 19.83.[152] In a study of penile tumescence, men were found most aroused by pictures of young adult females.[153]

Signals of fertility in women are often also seen as signals of youth. The evolutionary perspective proposes the idea that when it comes to sexual reproduction, the minimal parental investment required by men gives them the ability and want to simply reproduce 'as much as possible.'[154] It therefore makes sense that men are attracted to the features in women which signal youthfulness, and thus fertility.[154] Their chances of reproductive success are much higher than they would be should they pick someone olderand therefore less fertile.

This may explain why combating age declines in attractiveness occurs from a younger age in women than in men. For example, the removal of one's body hair is considered a very feminine thing to do.[155] This can be explained by the fact that aging results in raised levels of testosterone and thus, body hair growth. Shaving reverts one's appearance to a more youthful stage[155] and although this may not be an honest signal, men will interpret this as a reflection of increased fertile value. Research supports this, showing hairlessness to considered sexually attractive by men.[156]

Research has shown that most heterosexual men enjoy the sight of female breasts,[157] with a preference for large, firm breasts.[158] However, a contradictory study of British undergraduates found younger men preferred small breasts on women.[159] Smaller breasts were widely associated with youthfulness.[160] Cross-culturally, another study found "high variability" regarding the ideal breast size.[159] Some researchers in the United Kingdom have speculated that a preference for larger breasts may have developed in Western societies because women with larger breasts tend to have higher levels of the hormones estradiol and progesterone, which both promote fertility.[161]

A study showed that men prefer symmetrical breasts.[113][162] Breast symmetry may be particularly sensitive to developmental disturbances and the symmetry differences for breasts are large compared to other body parts. Women who have more symmetrical breasts tend to have more children.[163]

Historical literature often includes specific features of individuals or a gender that are considered desirable. These have often become a matter of convention, and should be interpreted with caution. In Arabian society in the Middle Ages, a component of the female beauty ideal was for women to have small breasts.[141] In Persian literature, beautiful women are said to have breasts like pomegranates or lemons.[138] In the Chinese text "Jeweled Chamber Secrets" (Chinese: ) from the Six Dynasties period, the ideal woman was described as having firm breasts.[142] In Sanskrit literature, beautiful women are often said to have breasts so large that they cause the women to bend a little bit from their weight.[164] In Middle English literature, beautiful women should have small breasts that are round like an apple or a pear.[54]

Biological anthropologist Helen E. Fisher of the Center for Human Evolution Studies in the Department of Anthropology of Rutgers University said that, "perhaps, the fleshy, rounded buttocks... attracted males during rear-entry intercourse."[166] Bobbi S. Low et al. of the School of Natural Resources and Environment at the University of Michigan, said the female "buttocks evolved in the context of females competing for the attention and parental commitment of powerful resource-controlling males" as an "honest display of fat reserves" that could not be confused with another type of tissue,[167] although T. M. Caro, professor in the Center for Population Biology and the Department of Wildlife, Fish, and Conservation Biology, at University of California, Davis, rejected that as being a necessary conclusion, stating that female fatty deposits on the hips improve "individual fitness of the female", regardless of sexual selection.[167]

In a 1995 study, black men were more likely than white men to use the words "big" or "large" to describe their conception of an attractive woman's posterior.[168]

Body Mass Index (BMI) is an important determinant to the perception of beauty.[169] Even though the Western ideal is for a thin woman, some cultures prefer plumper women,[129][170] which has been argued to support that attraction for a particular BMI merely is a cultural artifact.[170] The attraction for a proportionate body also influences an appeal for erect posture.[171] One cross-cultural survey comparing body-mass preferences among 300 of the most thoroughly studied cultures in the world showed that 81% of cultures preferred a female body size that in English would be described as "plump".[172]

Availability of food influences which female body size is attractive which may have evolutionary reasons. Societies with food scarcities prefer larger female body size than societies that have plenty of food. In Western society males who are hungry prefer a larger female body size than they do when not hungry.[173]

In the United States, women overestimate men's preferences for thinness in a mate. In one study, American women were asked to choose what their ideal build was and what they thought the build most attractive to men was. Women chose slimmer than average figures for both choices. When American men were independently asked to choose the female build most attractive to them, the men chose figures of average build. This indicates that women may be misled as to how thin men prefer women to be.[170] Some speculate that thinness as a beauty standard is one way in which women judge each other[135] and that thinness is viewed as prestigious for within-gender evaluations of other women.[citation needed] A reporter surmised that thinness is prized among women as a "sign of independence, strength and achievement."[135] Some implicated the fashion industry for the promulgation of the notion of thinness as attractive.[174]

East Asians have historically preferred women whose bodies had small features. For example, during the Spring and Autumn period of Chinese history, women in Chinese harems wanted to have a thin body in order to be attractive for the Chinese emperor. Later, during the Tang Dynasty, a less thin body type was seen as most attractive for Chinese women.[175] In Arabian society in the Middle Ages, a component of the female beauty ideal was for women to be slender like a "cane" or a "twig".[141] In the Chinese text "Jeweled Chamber Secrets" (Chinese: ) from the Six Dynasties period, the ideal woman was described as not being "large-boned".[142]

In the Victorian era, women who adhered to Victorian ideals were expected to limit their food consumption to attain the ideal slim figure.[176] In Middle English literature, "slender" women are considered beautiful.[54]

A WHR of 0.7 for women has been shown to correlate strongly with general health and fertility. Women within the 0.7 range have optimal levels of estrogen and are less susceptible to major diseases such as diabetes, heart disease, and ovarian cancers.[178] Women with high WHR (0.80 or higher) have significantly lower pregnancy rates than women with lower WHRs (0.700.79), independent of their BMIs.[179][180] Female waist-to-hip ratio (WHR) has been proposed by evolutionary psychologists to be an important component of human male mate choice, because this trait is thought to provide a reliable cue to a woman's reproductive value.[181]

Both men and women judge women with smaller waist-to-hip ratios more attractive.[182] Ethnic groups vary with regard to their ideal waist-to-hip ratio for women,[183] ranging from 0.6 in China,[184] to 0.8 or 0.9 in parts of South America and Africa,[185][186][187] and divergent preferences based on ethnicity, rather than nationality, have also been noted.[188][189] A study found the Machiguenga people, an isolated indigenous South American ethnic group, prefer women with high WHR (0.9).[190] The preference for heavier women, has been interpreted to belong to societies where there is no risk of obesity.[191]

In Chinese, the phrase "willow waist" (Chinese: ) is used to denote a beautiful woman by describing her waist as being slender like a willow branch.[142]

In the Victorian era, a small waist was considered the main trait of a beautiful woman.[176]

Most men tend to be taller than their female partner.[192] It has been found that, in Western societies, most men prefer shorter women. Having said this, height is a more important factor for a woman when choosing a man than it is for a man choosing a woman.[193] Men tend to view taller women as less attractive,[194] and people view heterosexual couples where the woman is taller to be less ideal.[194] Women who are 0.7 to 1.7 standard deviations below the mean female height have been reported to be the most reproductively successful,[195] since fewer tall women get married compared to shorter women.[194] However, in other ethnic groups, such as the Hadza, study has found that height is irrelevant in choosing a mate.[94]

In Middle English literature, 'tallness' is a characteristic of ideally beautiful women.[54]

A study using Polish participants by Sorokowski found 5% longer legs than average person leg to body ratio for both on man and woman was considered most attractive.[196] The study concluded this preference might stem from the influence of leggy runway models.[197] Another study using British and American participants, found "mid-ranging" leg-to-body ratios to be most ideal.[198]

A study by Swami et al. of British male and female undergraduates showed a preference for men with legs as long as the rest of their body and women with 40% longer legs than the rest of their body.[90] The researcher concluded that this preference might be influenced by American culture where long legged women are portrayed as more attractive.[90]

Marco Bertamini criticized the Swami et al. study for using a picture of the same person with digitally altered leg lengths which he felt would make the modified image appear unrealistic.[199] Bertamini also criticized the Swami study for only changing the leg length while keeping the arm length constant.[199] After accounting for these concerns in his own study, Bertamini's study which used stick figures also found a preference for women with proportionately longer legs than men.[199] When Bertamini investigated the issue of possible sexual dimorphism of leg length, he found two sources that indicated that men usually have slightly proportionately longer legs than women or that differences in leg length proportion may not exist between men and women.[199] Following this review of existing literature on the subject, he conducted his own calculations using data from 1774 men and 2208 women. Using this data, he similarly found that men usually have slightly proportionately longer legs than women or that differences in leg length proportion may not exist between men and women. These findings made him rule out the possibility that a preference for women with proportionately longer legs than men is due proportionately longer legs being a secondary sex characteristic of women.[199]

According to some studies, most men prefer women with small feet,[200][201] such as in ancient China where foot binding was practiced.[202]

In Jewish Rabbinic literature, the Rabbis considered small feet to be the ideal type of feet for women.[143]

Men have been found to prefer long-haired women.[111][203][204] An evolutionary psychology explanation for this is that malnutrition and deficiencies in minerals and vitamins causes loss of hair or hair changes. Hair therefore indicates health and nutrition during the last 23 years. Lustrous hair is also often a cross-cultural preference.[205] One study reported non-Asian men to prefer blondes and Asian men to prefer black-haired women.[204]

A component of the female beauty ideal in Persian literature is for women to have black hair,[138] which was also preferred in Arabian society in the Middle Ages.[141] In Middle English literature, curly hair is a necessary component of a beautiful woman.[54]

The way an individual moves can indicate health and even age and influence attractiveness.[205] A study reflecting the views of 700 individuals and that involved animated representations of people walking, found that the physical attractiveness of women increased by about 50 percent when they walked with a hip sway. Similarly, the perceived attractiveness of males doubled when they moved with a swagger in their shoulders.[206]

A preference for lighter-skinned women has remained prevalent over time, even in cultures without European contact, though exceptions have been found.[208] Anthropologist Peter Frost stated that since higher-ranking men were allowed to marry the perceived more attractive women, who tended to have fair skin, the upper classes of a society generally tended to develop a lighter complexion than the lower classes by sexual selection (see also Fisherian runaway).[104][208][209] In contrast, one study on men of the Bikosso tribe in Cameroon found no preference for attractiveness of females based on lighter skin color, bringing into question the universality of earlier studies that had exclusively focused on skin color preferences among non-African populations.[209]

Today, skin bleaching is not uncommon in parts of the world such as Africa,[210] and a preference for lighter-skinned women generally holds true for African Americans,[211] Latin Americans,[212] and Asians.[213] One exception to this has been in contemporary Western culture, where tanned skin used to be associated with the sun-exposed manual labor of the lower-class, but has generally been considered more attractive and healthier since the mid-20th century.[214][215][216][217][218]

More recent work has extended skin color research beyond preferences for lightness, arguing that redder (higher a* in the CIELab colour space) and yellower (higher b*) skin has healthier appearance.[107] These preferences have been attributed to higher levels of red oxygenated blood in the skin, which is associated with aerobic fitness and lack of cardiac and respiratory illnesses,[108] and to higher levels of yellow-red antioxidant carotenoids in the skin, indicative of more fruit and vegetables in the diet and, possibly more efficient immune and reproductive systems.[109]

Research has additionally shown that skin radiance or glowing skin indicates health, thus skin radiance influences perception of beauty and physical attractiveness.[219][220]

In Persian literature, beautiful women are said to have noses like hazelnuts.[138]

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Some people believe that calico cats are a breed, or that calico refers to a color of a cat. Since all cats are colored, calico refers to the pattern of how the coloring appears on the cat's coat.

According to a leading expert in Feline Genetics, Dr. Elizabeth A. Oltenacu of the Department of Animal Science at Cornell University:

"Early in its inception, a calico/tortie kitty is formed by a gene known as the white spotting factor. The white spotting factor effectively slows down the migration of cells across the kitten's body. One X-chromosome in every cell is switched off.

This is a random happenstance, and when a tortoiseshell kitten appears in the litter, you will see a mix of two colors of hair on the kitten.

In a calico kitten, the white spotting factor being present allows patches of cells with the same X chromosome shut-off to develop.

The results are patches of white, orange, and non-orange in the kitten. The more white in a calico, the larger the patches of white, orange and non-orange because the migration of cells in the embryo is slowed. Once the color is in patches, you can see the effect of the tabby genes in the orange patches."

Calico cats are overwhelmingly female. According to The Cat Fancier's Association Complete Cat Book; Persian calico cats have been accepted by CFA for years and calico Persians are always female and give birth to black-and-white or red and white bi-colored sons.

Genetically, two X chromosomes are needed to produce a calico coat, which is why the majority of calico cats are females. If the colors are black/orange upon the coat, then the cat is a calico cat. If the colors are blue/cream instead of the standard black/orange, then the cat is a muted calico.

Dr. Oltenacu further explains: "There's a gene on the X-chromosome that controls orange/non-orange color. One form (allele) determines orange, the other allele non-orange (usually black, but the actual color is determined by other genes on the autosomes). Neither form is dominant to the other, so a cat with one of each is a tortie.

It has to be female, as this requires 2 X-chromosomes. Sometimes an abnormal male is born XXY instead of the usual XY, so can be tortie.

Clearly, this male is the result of inaccurate separation of the chromosomes during egg or sperm formation. Usually, males are orange or non-orange, but not tortie as they have just one X-chromosome.

Now, if the cat also has the white-spotting gene (again autosomal, not on the sex chromosome). This will cause the color to be in patches, rather than the diffuse mix of orange and black in the tortie. Hence the calico."

If the majority of calico cats are female, then does this make male calicos valuable? For cat lovers, a calico cat, regardless of gender is valuable to the owner. Calico cats are quirky, independent, a tad stubborn and fun to be around.

It is clear that calico cats have captivated hearts of cat fanciers around the world. On October 1, 2001 the state of Maryland was so enamored with this delightful cat that they declared the calico cat as their official state cat.

The author wishes to acknowledge her great appreciation for Dr. Oltenacu's assistance in preparing this article.

Comments? Leave them using the form below. Questions? Please use the cat forums for those!

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In genetics, a mosaic (or mosaicism) means the presence of two different genotypes in an individual which developed from a single fertilized egg. As a result, the individual has two or more genetically different cell lines derived from a single zygote.[1]

Mosaicism may result from:

The phenomenon was discovered by Curt Stern. In 1936, he demonstrated that recombination, normal in meiosis, can also take place in mitosis.[2] When it does, it results in somatic (body) mosaics. These are organisms which contain two or more genetically distinct types of tissue.[3]

A genetic chimera is an organism composed of two or more sets of genetically distinct cells. Dispermic chimeras happen when two fertilized eggs fuse together. Mosaics are a different kind of chimerism: they originate from a single fertilized egg.

This is easiest to see with eye colours. When eye colours vary between the two eyes, or within one or both eyes, the condition is called heterochromia iridis (= 'different coloured iris'). It can have many different causes, both genetic and accidental. For example, David Bowie has the appearance of different eye colours due to an injury that caused one pupil to be permanently dilated.

On this page, only genetic mosaicism is discussed.

The most common cause of mosaicism in mammalian females is X-inactivation. Females have two X chromosomes (and males have only one). The two X chromosomes in a female are rarely identical. They have the same genes, but at some loci (positions) they may have different alleles (versions of the same gene).

In the early embryo, each cell independently and randomly inactivates one copy of the X chromosome.[4] This inactivation lasts the lifetime of the cell, and all the descendants of the cell inactivate that same chromosome.

This phenomenon shows in the colouration of calico cats and tortoiseshell cats. These females are heterozygous for the X-linked colour genes: the genes for their coat colours are carried on the X chromosome. X-inactivation causes groups of cells to carry either one or the other X-chromosome in an active state.[5]

X-inactivation is reversed in the female germline, so that all egg cells contain an active X chromosome.

Mosaicism refers to differences in the genotype of various cell populations in the same individual, but X-inactivation is an epigenetic change, a switching off of genes on one chromosome. It is not a change in the genotype.[6] Descendent cells of the embryo carry the same X-inactivation as the original cells. This may give rise to mild symptoms in female 'carriers' of X-linked genetic disorders.[7]

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Calico cats are domestic cats with a spotted or particolored coat that is predominantly white, with patches of two other colors (often, the two other colors are orange and black). Outside North America, the pattern is more usually called tortoiseshell-and-white. In the province of Quebec, Canada, they are sometimes called chatte d'Espagne (French for '(female) cat of Spain'). Other names include brindle, tricolor cat, tobi mi-ke (Japanese for 'triple fur'), and lapjeskat (Dutch for 'patches cat'); calicoes with diluted coloration have been called calimanco or clouded tiger. Occasionally, the tri-color calico coloration is combined with a tabby patterning. This calico patched tabby is called a caliby.[1]

"Calico" refers only to a color pattern on the fur, not to a breed.[2] Among the breeds whose standards allow calico coloration are the Manx, American Shorthair, British Shorthair, Persian, Japanese Bobtail, Exotic Shorthair, Siberian, Turkish Van, Turkish Angora and Norwegian Forest Cat.

Because genetic determination of coat colors in calico cats is linked to the X chromosome, calicoes are nearly always female, with one color linked to the maternal X chromosome and a second color linked to the paternal X chromosome.[2][3] Because males only have one X chromosome, a male calico would have to have a rare condition where they have three sex chromosomes (two X chromosomes and one Y chromosome) in order to be calico. In addition to other symptoms caused by the condition, these male calicos are often sterile.

There is also a calico cat referred to as a Dilute Calico. Dilute Calicos are not necessarily rare. They are recognized by their grey, silver, and gold colors instead if the traditional white, black, brown or red patched coat of a calico. Dilute calicos are also called light calicos; because they usually have no dark colored fur.

The coat pattern of calico cats does not define any breed, but occurs incidentally in cats that express a range of color patterns; accordingly the effect has no definitive historical background. However, the existence of patches in calico cats was traced to a certain degree by Neil Todd in a study determining the migration of domesticated cats along trade routes in Europe and Northern Africa.[4] The proportion of cats having the orange mutant gene found in calicoes was traced to the port cities along the Mediterranean in Greece, France, Spain and Italy, originating from Egypt.[5]

In genetic terms, calico cats are tortoiseshells in every way, except that in addition they express a white spotting gene. There is however one anomaly: as a rule of thumb the larger the areas of white, the fewer and larger the patches of ginger and dark or tabby coat.[citation needed] In contrast a non-white-spotted tortoiseshell usually has small patches of color or even something like a salt-and-pepper sprinkling. This reflects the genetic effects on relative speeds of migration of melanocytes and X-inactivation in the embryo.[6]

Serious study of calico cats seems to have begun about 1948 when Murray Barr and his graduate student E.G. Bertram noticed dark, drumstick-shaped masses inside the nuclei of nerve cells of female cats, but not in male cats. These dark masses became known as Barr bodies.[7] In 1959, Japanese cell biologist Susumu Ohno determined the Barr bodies were X chromosomes.[7] In 1961, Mary Lyon proposed the concept of X-inactivation: one of the two X chromosomes inside a female mammal shuts off.[7] She observed this in the coat color patterns in mice.[8]

Calico cats are almost always female because the locus of the gene for the orange/non-orange coloring is on the X chromosome. In the absence of other influences, such as color inhibition that causes white fur, the alleles present in those orange loci determine whether the fur is orange or not. Female cats like all female placental mammals normally have two X chromosomes. In contrast, male placental mammals, including chromosomally stable male cats, have one X and one Y chromosome.[2][7][9] Since the Y chromosome does not have any locus for the orange gene, there is no chance that an XY male could have both orange and non-orange genes together, which is what it takes to create tortoiseshell or calico coloring.[citation needed]

One exception is that in rare cases faulty cell division may leave an extra X chromosome in one of the gametes that produced the male cat. That extra X then is reproduced in each of his cells, a condition referred to as XXY, or Klinefelter syndrome. Such a combination of chromosomes could produce tortoiseshell or calico markings in the male, in the same way as XX chromosomes produce them in the female.[citation needed]

All but about one in three thousand of the rare calico or tortoiseshell male cats are sterile because of the chromosome abnormality, and breeders reject any exceptions for stud purposes because they generally are of poor physical quality and fertility. In any event, because the genetic conditions for calico coloring are X linked, a fertile male calico's coloring would not have any determination in the coloring of any male offspring (who would receive the Y, not the X chromosome from their father).

As Sue Hubble stated in her book Shrinking the Cat: Genetic Engineering before We Knew about Genes,

The mutation that gives male cats a ginger-colored coat and females ginger, tortoiseshell, or calico coats produced a particularly telling map. The orange mutant gene is found only on the X, or female, chromosome. As with humans, female cats have paired sex chromosomes, XX, and male cats have XY sex chromosomes. The female cat, therefore, can have the orange mutant gene on one X chromosome and the gene for a black coat on the other. The piebald gene is on a different chromosome. If expressed, this gene codes for white, or no color, and is dominant over the alleles that code for a certain color (i.e. orange or black), making the white spots on calico cats. If that is the case, those several genes will be expressed in a blotchy coat of the tortoiseshell or calico kind. But the male, with his single X chromosome, has only one of that particular coat-color gene: he can be not-ginger or he can be ginger (although some modifier genes can add a bit of white here and there), but unless he has a chromosomal abnormality he cannot be a calico cat.[5]

It is currently impossible to reproduce the fur patterns of calico cats by cloning. Penelope Tsernoglou wrote "This is due to an effect called x-linked inactivation which involves the random inactivation of one of the X chromosomes. Since all female mammals have two X chromosomes, one might wonder if this phenomenon could have a more widespread impact on cloning in the future."[10]

Calico cats may have already provided findings relating to physiological differences between male and female mammals. This insight may be one day broadened to the fields of psychology, psychiatry, sociology, biology and medicine as more information becomes available regarding the complete effect of random X-inactivation in female mammals.[7][9][11]

Cats of this coloration are believed to bring good luck in the folklore of many cultures.[12] In the United States, these are sometimes referred to as money cats.[13] A cat of the calico coloration is also the state cat of Maryland in the United States.[14] In the late nineteenth century, Eugene Field published "The Duel", a beloved poem for children also known as "The Gingham Dog and the Calico Cat." In Japan, the Maneki-Neko figures depict Calico cats, bringing good luck.

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Female () is the sex of an organism, or a part of an organism, that produces non-mobile ova (egg cells). Most female mammals, including female humans, have two X chromosomes.

The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male. A female individual cannot reproduce sexually without access to the gametes of a male (an exception is parthenogenesis). Some organisms can reproduce both sexually and asexually.

There is no single genetic mechanism behind sex differences in different species and the existence of two sexes seems to have evolved multiple times independently in different evolutionary lineages.[1] Patterns of sexual reproduction include

Other than the defining difference in the type of gamete produced, differences between males and females in one lineage cannot always be predicted by differences in another. The concept is not limited to animals; egg cells are produced by chytrids, diatoms, water moulds and land plants, among others. In land plants, female and male designate not only the egg- and sperm-producing organisms and structures, but also the structures of the sporophytes that give rise to male and female plants.

The word female comes from the Latin femella, the diminutive form of femina, meaning "woman". It is not etymologically related to the word male, but in the late 14th century the spelling was altered in English to parallel the spelling of male.[3]

A distinguishing characteristic of the class Mammalia is the presence of mammary glands. The mammary glands are modified sweat glands that produce milk, which is used to feed the young for some time after birth. Only mammals produce milk. Mammary glands are most obvious in humans, as the female human body stores large amounts of fatty tissue near the nipples, resulting in prominent breasts. Mammary glands are present in all mammals, although they are vestigial in the male of the species.

Most mammalian females have two copies of the X chromosome as opposed to the male which carries only one X and one smaller Y chromosome (but some mammals, such as the Platypus, have different combinations). To compensate for the difference in size, one of the female's X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactived in marsupials. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Intersex conditions can also give rise to other combinations, such as XO or XXX in mammals, which are still considered as female so long as they do not contain a Y-chromosome. However, these conditions frequently result in sterility.

Mammalian females bear live young (with the rare exception of monotremes, which lay eggs). Some non-mammalian species, such as guppies, have analogous reproductive structures; and some other non-mammals, such as sharks, whose eggs hatch inside their bodies, also have the appearance of bearing live young.

A common symbol used to represent the female sex is (Unicode: U+2640 Alt codes: Alt+12), a circle with a small cross underneath. According to Schott,[4] the most established view is that the male and female symbols "are derived from contractions in Greek script of the Greek names of these planets, namely Thouros (Mars) and Phosphoros (Venus). These derivations have been traced by Renkama[5] who illustrated how Greek letters can be transformed into the graphic male and female symbols still recognised today." Thouros was abbreviated by , and Phosphoros by , both in the handwriting of alchemists so somewhat different from the Greek symbols we know. These abbreviations were contracted into the modern symbols.

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals have both male and female reproductive organs.

The sex of most mammals, including humans, is genetically determined by the XY sex-determination system where males have X and Y (as opposed to X and X) sex chromosomes. During reproduction, the male contributes either an X sperm or a Y sperm, while the female always contributes an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female. The ZW sex-determination system, where males have ZZ (as opposed to ZW) sex chromosomes, is found in birds, reptiles and some insects and other organisms. Members of Hymenoptera, such as ants and bees, are determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid.[citation needed]

The young of some species develop into one sex or the other depending on local environmental conditions, e.g. many crocodilians' sex is influenced by the temperature of their eggs. Other species (such as the goby) can transform, as adults, from one sex to the other in response to local reproductive conditions (such as a shortage of males).

Ayers, Donald M. English Words from Latin and Greek Elements. Second Edition. 1986. University of Arizona Press. United States.

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A male () organism is the physiological sex that produces sperm. Each spermatozoon can fuse with a larger female gamete, or ovum, in the process of fertilization. A male cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs.

Not all species share a common sex-determination system. In most animals, including humans, sex (as opposed to gender) is determined genetically, but in some species it can be determined due to social, environmental or other factors. For example, Cymothoa exigua changes sex depending on the number of females present in the vicinity.[1]

The existence of two sexes seems to have been selected independently across different evolutionary lineages (see convergent evolution). The repeated pattern is sexual reproduction in isogamous species with two or more mating types with gametes of identical form and behavior (but different at the molecular level) to anisogamous species with gametes of male and female types to oogamous species in which the female gamete is very much larger than the male and has no ability to move. There is a good argument that this pattern was driven by the physical constraints on the mechanisms by which two gametes get together as required for sexual reproduction.[2]

Accordingly, sex is defined operationally across species by the type of gametes produced (i.e.: spermatozoa vs. ova) and differences between males and females in one lineage are not always predictive of differences in another.

Male/female dimorphism between organisms or reproductive organs of different sexes is not limited to animals; male gametes are produced by chytrids, diatoms and land plants, among others. In land plants, female and male designate not only the female and male gamete-producing organisms and structures but also the structures of the sporophytes that give rise to male and female plants. As of the year 2012, the United Arab Emirates has the highest ratio of human males in the world, followed by Qatar.[3]

A common symbol used to represent the male sex is the Mars symbol, (Unicode: U+2642 Alt codes: Alt+11)a circle with an arrow pointing northeast. The symbol is identical to the planetary symbol of Mars. It was first used to denote sex by Carl Linnaeus in 1751. The symbol is often called a stylized representation of the Roman god Mars' shield and spear. According to Stearn, however, all the historical evidence favours that it is derived from , the contraction of the Greek name for the planet, Thouros.[4]

The sex of a particular organism may be determined by a number of factors. These may be genetic or environmental, or may naturally change during the course of an organism's life. Although most species with male and female sexes have individuals that are either male or female, hermaphroditic animals, such as worms, have both male and female reproductive organs.

Most mammals, including humans, are genetically determined as such by the XY sex-determination system where males have an XY (as opposed to XX) sex chromosome. It is also possible in a variety of species, including human beings, to be XXY or have other intersex/hermaphroditic qualities, though one would still be considered genotypically (if not necessarily phenotypically) male so long as one has a Y-chromosome. During reproduction, a male can give either an X sperm or a Y sperm, while a female can only give an X egg. A Y sperm and an X egg produce a male, while an X sperm and an X egg produce a female.

The part of the Y-chromosome which is responsible for maleness is the sex-determining region of the Y-chromosome, the SRY. The SRY activates Sox9, which forms feedforward loops with FGF9 and PGD2 in the gonads, allowing the levels of these genes to stay high enough in order to cause male development;[5] for example, Fgf9 is responsible for development of the spermatic cords and the multiplication of Sertoli cells, both of which are crucial to male sexual development.[6]

The ZW sex-determination system, where males have a ZZ (as opposed to ZW) sex chromosome may be found in birds and some insects (mostly butterflies and moths) and other organisms. Members of the insect order Hymenoptera, such as ants and bees, are often determined by haplodiploidy, where most males are haploid and females and some sterile males are diploid.[citation needed]

In some species of reptiles, including alligators, sex is determined by the temperature at which the egg is incubated. Other species, such as some snails, practice sex change: adults start out male, then become female. In tropical clown fish, the dominant individual in a group becomes female while the other ones are male.[citation needed]

In some arthropods, sex is determined by infection. Bacteria of the genus Wolbachia alter their sexuality; some species consist entirely of ZZ individuals, with sex determined by the presence of Wolbachia.[citation needed]

In those species with two sexes, males may differ from females in ways other than production of spermatozoa. In many insects and fish the male is smaller than the female. In seed plants, which exhibit alternation of generations, the female and male parts are both included within the sporophyte sex organ of a single organism. In mammals, including humans, males are typically larger than females. In birds, the male often exhibits a colorful plumage that attracts females.[citation needed]

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acquired trait: A phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next generation (for example, the large muscles of a weightlifter).

adaptation: Any heritable characteristic of an organism that improves its ability to survive and reproduce in its environment. Also used to describe the process of genetic change within a population, as influenced by natural selection.

adaptive landscape: A graph of the average fitness of a population in relation to the frequencies of genotypes in it. Peaks on the landscape correspond to genotypic frequencies at which the average fitness is high, valleys to genotypic frequencies at which the average fitness is low. Also called a fitness surface.

adaptive logic: A behavior has adaptive logic if it tends to increase the number of offspring that an individual contributes to the next and following generations. If such a behavior is even partly genetically determined, it will tend to become widespread in the population. Then, even if circumstances change such that it no longer provides any survival or reproductive advantage, the behavior will still tend to be exhibited -- unless it becomes positively disadvantageous in the new environment.

adaptive radiation: The diversification, over evolutionary time, of a species or group of species into several different species or subspecies that are typically adapted to different ecological niches (for example, Darwin's finches). The term can also be applied to larger groups of organisms, as in "the adaptive radiation of mammals."

adaptive strategies: A mode of coping with competition or environmental conditions on an evolutionary time scale. Species adapt when succeeding generations emphasize beneficial characteristics.

agnostic: A person who believes that the existence of a god or creator and the nature of the universe is unknowable.

algae: An umbrella term for various simple organisms that contain chlorophyll (and can therefore carry out photosynthesis) and live in aquatic habitats and in moist situations on land. The term has no direct taxonomic significance. Algae range from macroscopic seaweeds such as giant kelp, which frequently exceeds 30 m in length, to microscopic filamentous and single-celled forms such as Spirogyra and Chlorella.

allele: One of the alternative forms of a gene. For example, if a gene determines the seed color of peas, one allele of that gene may produce green seeds and another allele produce yellow seeds. In a diploid cell there are usually two alleles of any one gene (one from each parent). Within a population there may be many different alleles of a gene; each has a unique nucleotide sequence.

allometry: The relation between the size of an organism and the size of any of its parts. For example, an allometric relation exists between brain size and body size, such that (in this case) animals with bigger bodies tend to have bigger brains. Allometric relations can be studied during the growth of a single organism, between different organisms within a species, or between organisms in different species.

allopatric speciation: Speciation that occurs when two or more populations of a species are geographically isolated from one another sufficiently that they do not interbreed.

allopatry: Living in separate places. Compare with sympatry.

amino acid: The unit molecular building block of proteins, which are chains of amino acids in a certain sequence. There are 20 main amino acids in the proteins of living things, and the properties of a protein are determined by its particular amino acid sequence.

amino acid sequence: A series of amino acids, the building blocks of proteins, usually coded for by DNA. Exceptions are those coded for by the RNA of certain viruses, such as HIV.

ammonoid: Extinct relatives of cephalopods (squid, octopi, and chambered nautiluses), these mollusks had coiled shells and are found in the fossil record of the Cretaceous period.

amniotes: The group of reptiles, birds, and mammals. These all develop through an embryo that is enclosed within a membrane called an amnion. The amnion surrounds the embryo with a watery substance, and is probably an adaptation for breeding on land.

amphibians: The class of vertebrates that contains the frogs, toads, newts, and salamanders. The amphibians evolved in the Devonian period (about 370 million years ago) as the first vertebrates to occupy the land. They have moist scaleless skin which is used to supplement the lungs in gas exchange. The eggs are soft and vulnerable to drying, therefore reproduction commonly occurs in water. Amphibian larvae are aquatic, and have gills for respiration; they undergo metamorphosis to the adult form. Most amphibians are found in damp environments and they occur on all continents except Antarctica.

analogous structures: Structures in different species that look alike or perform similar functions (e.g., the wings of butterflies and the wings of birds) that have evolved convergently but do not develop from similar groups of embryological tissues, and that have not evolved from similar structures known to be shared by common ancestors. Contrast with homologous structures. Note: The recent discovery of deep genetic homologies has brought new interest, new information, and discussion to the classical concepts of analogous and homologous structures.

anatomy: (1) The structure of an organism or one of its parts. (2) The science that studies those structures.

ancestral homology: Homology that evolved before the common ancestor of a set of species, and which is present in other species outside that set of species. Compare with derived homology.

anthropoid: A member of the group of primates made up of monkeys, apes, and humans.

antibacterial: Having the ability to kill bacteria.

antibiotics: Substances that destroy or inhibit the growth of microorganisms, particularly disease-causing bacteria.

antibiotic resistance: A heritable trait in microorganisms that enables them to survive in the presence of an antibiotic.

aperture: Of a camera, the adjustable opening through which light passes to reach the film. The diameter of the aperture determines the intensity of light admitted. The pupil of a human eye is a self-adjusting aperture.

aquatic: Living underwater.

arboreal: Living in trees.

archeology: The study of human history and prehistory through the excavation of sites and the analysis of physical remains, such as graves, tools, pottery, and other artifacts.

archetype: The original form or body plan from which a group of organisms develops.

artifact: An object made by humans that has been preserved and can be studied to learn about a particular time period.

artificial selection: The process by which humans breed animals and cultivate crops to ensure that future generations have specific desirable characteristics. In artificial selection, breeders select the most desirable variants in a plant or animal population and selectively breed them with other desirable individuals. The forms of most domesticated and agricultural species have been produced by artificial selection; it is also an important experimental technique for studying evolution.

asexual reproduction: A type of reproduction involving only one parent that ususally produces genetically identical offspring. Asexual reproduction occurs without fertilization or genetic recombination, and may occur by budding, by division of a single cell, or by the breakup of a whole organism into two or more new individuals.

assortative mating: The tendency of like to mate with like. Mating can be assortative for a certain genotype (e.g., individuals with genotype AA tend to mate with other individuals of genotype AA) or phenotype (e.g., tall individuals mate with other tall individuals).

asteroid: A small rocky or metallic body orbitting the Sun. About 20,000 have been observed, ranging in size from several hundred kilometers across down to dust particles.

atheism: The doctrine or belief that there is no god.

atomistic: (as applied to theory of inheritance) Inheritance in which the entities controlling heredity are relatively distinct, permanent, and capable of independent action. Mendelian inheritance is an atomistic theory because in it, inheritance is controlled by distinct genes.

australopithecine: A group of bipedal hominid species belonging to the genus Australopithecus that lived between 4.2 and 1.4 mya.

Australopithecus afarensis: An early australopithecine species that was bipedal; known fossils date between 3.6 and 2.9 mya (for example, Lucy).

autosome: Any chromosome other than a sex chromosome.

avian: Of, relating to, or characteristic of birds (members of the class Aves).

bacteria: Tiny, single-celled, prokaryotic organisms that can survive in a wide variety of environments. Some cause serious infectious diseases in humans, other animals, and plants.

base: The DNA molecule is a chain of nucleotide units; each unit consists of a backbone made of a sugar and a phosphate group, with a nitrogenous base attached. The base in a unit is one of adenine (A), guanine (G), cytosine (C), or thymine (T). In RNA, uracil (U) is used instead of thymine. A and G belong to the chemical class called purines; C, T, and U are pyrimidines.

Batesian mimicry: A kind of mimicry in which one non-poisonous species (the Batesian mimic) mimics another poisonous species.

belemnite: An extinct marine invertebrate that was related to squid, octopi, and chambered nautiluses. We know from the fossil record that belemnites were common in the Jurassic period and had bullet-shaped internal skeletons.

big bang theory: The theory that states that the universe began in a state of compression to infinite density, and that in one instant all matter and energy began expanding and have continued expanding ever since.

biodiversity (or biological diversity): A measure of the variety of life, biodiversity is often described on three levels. Ecosystem diversity describes the variety of habitats present; species diversity is a measure of the number of species and the number of individuals of each species present; genetic diversity refers to the total amount of genetic variability present.

bioengineered food: Food that has been produced through genetic modification using techniques of genetic engineering.

biogenetic law: Name given by Haeckel to recapitulation.

biogeography: The study of patterns of geographical distribution of plants and animals across Earth, and the changes in those distributions over time.

biological species concept: The concept of species, according to which a species is a set of organisms that can interbreed among each other. Compare with cladistic species concept, ecological species concept, phenetic species concept, and recognition species concept.

biometrics: The quantitative study of characters of organisms.

biosphere: The part of Earth and its atmosphere capable of sustaining life.

bipedalism: Of hominids, walking upright on two hind legs; more generally, using two legs for locomotion.

bivalve: A mollusk that has a two-part hinged shell. Bivalves include clams, oysters, scallops, mussels, and other shellfish.

Blackmore, Susan: A psychologist interested in memes and the theory of memetics, evolutionary theory, consciousness, the effects of meditation, and why people believe in the paranormal. A recent book, The Meme Machine, offers an introduction to the subject of memes.

blending inheritance: The historically influential but factually erroneous theory that organisms contain a blend of their parents' hereditary factors and pass that blend on to their offspring. Compare with Mendelian inheritance.

botanist: A scientist who studies plants.

brachiopod: Commonly known as "lamp shells," these marine invertebrates resemble bivalve mollusks because of their hinged shells. Brachiopods were at their greatest abundance during the Paleozoic and Mesozoic eras.

Brodie, Edmund D., III: A biologist who studies the causes and evolutionary implications of interactions among traits in predators and their prey. Much of his work concentrates on the coevolutionary arms race between newts that posess tetrodotoxin, one of the most potent known toxins, and the resistant garter snakes who prey on them.

Brodie, Edmund D., Jr.: A biologist recognized internationally for his work on the evolution of mechanisms in amphibians that allow them to avoid predators. These mechanisms include toxins carried in skin secretions, coloration, and behavior.

Bruner, Jerome: A psychologist and professor at Harvard and Oxford Universities, and a prolific author whose book, The Process of Education, encouraged curriculum innovation based on theories of cognitive development.

bryozoan: A tiny marine invertebrate that forms a crust-like colony; colonies of bryozoans may look like scaly sheets on seaweed.

Burney, David: A biologist whose research has focused on endangered species, paleoenvironmental studies, and causes of extinction in North America, Africa, Madagascar, Hawaii, and the West Indies.

carbon isotope ratio: A measure of the proportion of the carbon-14 isotope to the carbon-12 isotope. Living material contains carbon-14 and carbon-12 in the same proportions as exists in the atmosphere. When an organism dies, however, it no longer takes up carbon from the atmosphere, and the carbon-14 it contains decays to nitrogen-14 at a constant rate. By measuring the carbon-14-to-carbon-12 ratio in a fossil or organic artifact, its age can be determined, a method called radiocarbon dating. Because most carbon-14 will have decayed after 50,000 years, the carbon isotope ratio is mainly useful for dating fossils and artifacts younger than this. It cannot be used to determine the age of Earth, for example.

carnivorous: Feeding largely or exclusively on meat or other animal tissue.

Carroll, Sean: Developmental geneticist with the Howard Hughes Medical Institute and professor at the University of Wisconsin-Madison. From the large-scale changes that distinguish major animal groups to the finely detailed color patterns on butterfly wings, Dr. Carroll's research has centered on those genes that create the "molecular blueprint" for body pattern and play major roles in the origin of new features. Coauthor, with Jennifer Grenier and Scott Weatherbee, of From DNA to Diversity: Molecular Genetics and the Evolution of Animal Design.

Carson, Rachel: A scientist and writer fascinated with the workings of nature. Her best-known publication, Silent Spring, was written over the years 1958 to 1962. The book looks at the effects of insecticides and pesticides on songbird populations throughout the United States. The publication helped set off a wave of environmental legislation and galvanized the emerging ecological movement.

Castle, W.E.: An early experimental geneticist, his 1901 paper was the first on Mendelism in America. His Genetics of Domestic Rabbits, published in 1930 by Harvard University Press, covers such topics as the genes involved in determining the coat colors of rabbits and associated mutations.

cell: The basic structural and functional unit of most living organisms. Cell size varies, but most cells are microscopic. Cells may exist as independent units of life, as in bacteria and protozoans, or they may form colonies or tissues, as in all plants and animals. Each cell consists of a mass of protein material that is differentiated into cytoplasm and nucleoplasm, which contains DNA. The cell is enclosed by a cell membrane, which in the cells of plants, fungi, algae, and bacteria is surrounded by a cell wall. There are two main types of cell, prokaryotic and eukaryotic.

Cenozoic: The era of geologic time from 65 mya to the present, a time when the modern continents formed and modern animals and plants evolved.

centromere: A point on a chromosome that is involved in separating the copies of the chromosome produced during cell division. During this division, paired chromosomes look somewhat like an X, and the centromere is the constriction in the center.

cephalopod: Cephalopods include squid, octopi, cuttlefish, and chambered nautiluses. They are mollusks with tentacles and move by forcing water through their bodies like a jet.

character: Any recognizable trait, feature, or property of an organism. In phylogenetic studies, a character is a feature that is thought to vary independantly of other features, and to be derived from a corresponding feature in a common ancestor of the organisms being studied. A "character state" is one of the possible alternative conditions of the character. For example, "present" and "absent" are two states of the character "hair" in mammals. Similarly, a particular position in a DNA sequence is a character, and A, T, C, and G are its possible states (see bases.)

character displacement: The increased difference between two closely related species where they live in the same geographic region (sympatry) as compared with where they live in different geographic regions (allopatry). Explained by the relative influences of intra- and inter-specific competition in sympatry and allopatry.

chloroplast: A structure (or organelle) found in some cells of plants; its function is photosynthesis.

cholera: An acute infectious disease of the small intestine, caused by the bacterium Vibrio cholerae which is transmitted in drinking water contaminated by feces of a patient. After an incubation period of 1-5 days, cholera causes severe vomiting and diarrhea, which, if untreated, leads to dehydration that can be fatal.

chordate: A member of the phylum Chordata, which includes the tunicates, lancelets, and vertebrates. They are animals with a hollow dorsal nerve cord; a rodlike notochord that forms the basis of the internal skeleton; and paired gill slits in the wall of the pharynx behind the head, although in some chordates these are apparent only in early embryonic stages. All vertebrates are chordates, but the phylum also contains simpler types, such as sea-squirts, in which only the free-swimming larva has a notochord.

chromosomal inversion: See inversion.

chromosome: A structure in the cell nucleus that carries DNA. At certain times in the cell cycle, chromosomes are visible as string-like entities. Chromosomes consist of the DNA with various proteins, particularly histones, bound to it.

chronology: The order of events according to time.

Clack, Jenny: A paleontologist at Cambridge University in the U.K., Dr. Clack studies the origin, phylogeny, and radiation of early tetrapods and their relatives among the lobe-finned fish. She is interested in the timing and sequence of skeletal and other changes which occurred during the transition, and the origin and relationships of the diverse tetrapods of the late Paleozoic.

clade: A set of species descended from a common ancestral species. Synonym of monophyletic group.

cladism: Phylogenetic classification. The members of a group in a cladistic classification share a more recent common ancestor with one another than with the members of any other group. A group at any level in the classificatory hierarchy, such as a family, is formed by combining a subgroup at the next lowest level (the genus, in this case) with the subgroup or subgroups with which it shares its most recent common ancestor. Compare with evolutionary classification and phenetic classification.

cladistic species concept: The concept of species, according to which a species is a lineage of populations between two phylogenetic branch points (or speciation events). Compare with biological species concept, ecological species concept, phenetic species concept, and recognition species concept.

cladists: Evolutionary biologists who seek to classify Earth's life forms according to their evolutionary relationships, not just overall similarity.

cladogram: A branching diagram that illustrates hypotheses about the evolutionary relationships among groups of organisms. Cladograms can be considered as a special type of phylogenetic tree that concentrates on the order in which different groups branched off from their common ancestors. A cladogram branches like a family tree, with the most closely related species on adjacent branches.

class: A category of taxonomic classification between order and phylum, a class comprises members of similar orders. See taxon.

classification: The arrangement of organisms into hierarchical groups. Modern biological classifications are Linnaean and classify organisms into species, genus, family, order, class, phylum, kingdom, and certain intermediate categoric levels. Cladism, evolutionary classification, and phenetic classification are three methods of classification.

cline: A geographic gradient in the frequency of a gene, or in the average value of a character.

clock: See molecular clock.

clone: A set of genetically identical organisms asexually reproduced from one ancestral organism.

coadaptation: Beneficial interaction between (1) a number of genes at different loci within an organism, (2) different parts of an organism, or (3) organisms belonging to different species.

codon: A triplet of bases (or nucleotides) in the DNA coding for one amino acid. The relation between codons and amino acids is given by the genetic code. The triplet of bases that is complementary to a condon is called an anticodon; conventionally, the triplet in the mRNA is called the codon and the triplet in the tRNA is called the anticodon.

coelacanth: Although long thought to have gone extinct about 65 million years ago, one of these deep-water, lungless fish was caught in the 1930s. Others have since been caught and filmed in their natural habitat.

coevolution: Evolution in two or more species, such as predator and its prey or a parasite and its host, in which evolutionary changes in one species influence the evolution of the other species.

cognitive: Relating to cognition, the mental processes involved in the gathering, organization, and use of knowledge, including such aspects as awareness, perception, reasoning, and judgement. The term refers to any mental "behaviors" where the underlying characteristics are abstract in nature and involve insight, expectancy, complex rule use, imagery, use of symbols, belief, intentionality, problem-solving, and so forth.

common ancestor: The most recent ancestral form or species from which two different species evolved.

comparative biology: The study of patterns among more than one species.

comparative method: The study of adaptation by comparing many species.

concerted evolution: The tendency of the different genes in a gene family to evolve in concert; that is, each gene locus in the family comes to have the same genetic variant.

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