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Archive for the ‘Male Genetics’ Category

Twins Separated at Birth Reveal Staggering Influence of …

WASHINGTON Jim Lewis and Jim Springer were identical twins raised apart from the age of 4 weeks. When the twins were finally reunited at the age of 39 in 1979, they discovered they both suffered from tension headaches, were prone to nail biting, smoked Salem cigarettes, drove the same type of car and even vacationed at the same beach in Florida.

The culprit for the odd similarities? Genes.

Genes can help explain why someone is gay or straight, religious or not, brainy or not, and even whether they’re likely to develop gum disease, one psychologist explains.

Such broad-ranging genetic effects first came to light in a landmark study Minnesota Twin Family Study conducted from 1979 to 1999, which followed identical and fraternal twins who were separated at an early age. [Seeing Double: 8 Fascinating Facts About Twins]

“We were surprised by certain behaviors that showed a genetic influence, such as religiosity [and] social attitudes,” said Nancy Segal, an evolutionary psychologist at California State University, Fullerton, who was part of the study for nine years. “Those surprised us, because we thought those certainly must come from the family [environment],” Segal told Live Science. Segal described the groundbreaking research on Aug. 7 here at a meeting of the American Psychological Association.

Born together, raised apart

Researchers at the University of Minnesota, led by Thomas Bouchard, launched the landmark study in 1979. Over the course of 20 years, they studied 137 pairs of twins 81 pairs of identical twins (twins who developed from one egg that split in two), and 56 pairs of fraternal twins (twins who developed from two eggs fertilized by two different sperm).

The Jim twins were probably the most famous set of twins involved in the study, but other pairs were equally fascinating. One pair of female twins in the study were separated from each other at 5 months old, and weren’t reunited until age 78, making them the world’s longest separated pair in Guinness World Records.

The Minnesota study resulted in more than 170 individual studies focusing on different medical and psychological characteristics.

In one study, the researchers took photographs of the twins, and found that identical twins would stand the same way, while fraternal twins had different postures.

Another study of four pairs of twins found that genetics had a stronger influence on sexual orientation in male twins than in female twins. A recent study in Sweden of 4,000 pairs of twins has replicated these findings, Segal said. [5 Myths About Gay People Debunked]

Nature vs. nurture

A 1986 study that was part of the larger Minnesota study found that genetics plays a larger role on personality than previously thought. Environment affected personality when twins were raised apart, but not when they were raised together, the study suggested.

Reporter Daniel Goleman wrote in The New York Times at the time that genetic makeup was more influential on personality than child rearing a finding he said would launch “fierce debate.”

“We never said [family environment] didn’t matter,” Segal said at the APA meeting. “We just made the point that environment works in ways we hadn’t expected.”

Another study, commissioned by the editor of the journal Science, looked at genetics and IQ. The Minnesota researchers found that about 70 percent of IQ variation across the twin population was due to genetic differences among people, and 30 percent was due to environmental differences. The finding received both praise and criticism, but an updated study in 2009 containing new sets of twins found a similar correlation between genetics and IQ.

Moreover, a study in 1990 found that genetics account for 50 percent of the religiosity among the population in other words, both identical twins raised apart were more likely to be religious or to be not religious, compared with unrelated individuals.

Other studies found a strong genetic influence on dental or gum health. That research helped to show that gum disease isn’t just caused by bacteria, it also has a genetic component, Segal said.

Another study found that happiness and well-being had a 50 percent genetic influence.

In another study, researchers surveyed the separated twins about how close they felt to their newfound sibling. Among identical twins, 80 percent of those surveyed reported feeling closer and more familiar with their twin than they did to their best friends, suggesting a strong genetic component in the bond between identical twins.

The Minnesota study gave scientists a new understanding of the role of genes and environment on human development, Segal said. In the future, twin studies will aim to link specific genes to specific behaviors, as well as investigate epigenetics what turns genes on or off, she said.

Segal, who wrote a book about the study called “Born Together Reared Apart: The Landmark Minnesota Twins Study” (Harvard University Press, 2012), is now doing a prospective study of Chinese twins raised apart, often in different countries, by adoptive families.

Follow Tanya Lewis on Twitterand Google+. Follow us @livescience, Facebook& Google+. Original article onLive Science.

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Twins Separated at Birth Reveal Staggering Influence of …

Cohen wins Gates grant for her new take on male contraception – Cornell Chronicle

In time, men may have a new way to prevent pregnancy, thanks to the innovative thinking of a Cornell geneticist.

Paula Cohen, professor of genetics in the College of Veterinary Medicine, has won a $100,000 grant from the Bill & Melinda Gates Foundation to develop a radical approach to contraception an area that has remained static for many years.

Thats whats truly innovative here: We are targeting a stage in the reproductive cycle thats poorly understood, Cohen said.

An expert in the genetics of fertility, Cohen was one of 28 researchers, chosen from 1,600 applicants from around the world, awarded a Grand Challenges Explorations grant, funded by the Gates Foundation. The grant supports innovative thinkers worldwide to explore ideas that can break the mold in how we solve persistent global health and development challenges. Successful projects have the opportunity to receive a follow-on grant of up to $1 million.

Cohens project will look at meiosis, a poorly understood stage of development in which a sperm cells DNA is halved. When the sperm fertilizes an egg which also contains only one half of its chromosomes the resulting embryo is restored to the full number of chromosomes.

Ive always thought that if we can stop those cells from actually getting into meiosis, youd have a really good contraceptive, Cohen said.

There are several reasons why this stage of sperm cell development is a better target for contraception than others, she said.

Traditionally, contraceptives have tried to block the sperm from getting to the egg, with barriers like condoms and spermicide. Thats shutting the stable door after the horse has bolted, Cohen said. If a single swimmer gets out, it still has the potential to fertilize an egg, and you cant always prevent that from happening.

Hormonal approaches, like birth control pills, have their own drawbacks. Cohen believes they are not always good for women. And the development of a male birth control pill has always been scorned by men who fear that their libido and/or male sexual characteristics will be diminished.

And contraceptives that target the sperm cell in the testis at a late stage of development might result in mutant sperm and thus birth defects.

Her new approach, centering on the sperm cells entry into meiosis, before it even leaves the testis, offers several benefits.

For example, should one sperm sneak its way through to meiosis, the surveillance machinery present during meiosis would get rid of that solitary cell; in other words, the meiotic process itself would check for escapers. And unlike later stages of sperm cell development, the cells entry into meiosis is accessible to blood-borne factors such as drugs.

The problem is, we know very little about meiosis, because its a very hard stage to target biologically or molecularly, she said. Only recently have we started to gather the tools to be able to look at it. One tool Cohen will use is called CRISPR/Cas9, a genome editing technology that allows genes to be modified permanently and very rapidly.

She has three goals. First, shell try to prove she can get the sperm cells to go into meiosis in culture. Second, shell monitor the cells entry, by engineering what are known as reporter mice, whose cells turn green or red depending on whether or not they have entered meiosis. Third, and as proof-of-principle, shell try to manipulate two genes that are known to affect a cells entry into meiosis.

One gene is required for sperm stem cell maintenance in the testes; if it is deleted, cells rapidly progress into meiosis. The second gene is required for the sperm cell to enter meiosis; it if is blocked, the cells stop developing. So weve got a gene that should accelerate their entry into meiosis and one that should slow it down, Cohen said.

If she can manipulate those genes, that opens the door to the possibility of finding others. There could be hundreds of genes that control this process, she said. We just need to find them and begin to ask whether they are potential contraceptive targets.

This is not the type of science that would qualify for funding through traditional agencies like the National Institutes of Health, Cohen said.

Its very out there, its very risky, and thats what the Gates Foundation is going for, she said. They want you to come up with ideas that are truly revolutionary.

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Cohen wins Gates grant for her new take on male contraception – Cornell Chronicle

A Florida higher-ed official said women’s genetics may be keeping … – Washington Post

A Florida college official said Tuesday that women make less money than men because genetically they might lack the skills to negotiate for better pay.

Edward Morton ofthe State University System of Florida made the comments during a board meeting in which members talked about closing the wage gap between male and femalegraduates of the states public university system.Morton, chair of the boards Strategic Planning Committee and a financial adviser from Naples, Fla., said,according to Politico:

Something that were doing in Naples some of our high school students, were actually talking about incorporating negotiating and negotiating skill into curriculum so that the women are given maybe some of it is genetic, I dont know, Im not smart enough to know the difference but I do know that negotiating skills can be something that can be honed, and they can improve. Perhaps we can address than in all of our various curriculums through the introduction of negotiating skill, and maybe that would have a bearing on these things.

Morton apologized for his comment in an email sent to fellow board members shortly after the meeting.

I chose my words poorly. My belief is that women and men should be valued equally in the workplace, he said, adding that the universitys goal is to teach all students how to better negotiate their salaries.

[Utah Republican argues against equal pay for women: Its bad for families and society]

Gov. Rick Scott, who appointed Morton to the board, was among those who quickly criticized Morton for hiscomments. Lauren Schenone, a spokeswoman for Scott, said in a statement that as a father of two daughters, the governorabsolutely does not agree with Mortonscomments.

Gwen Graham, whos seeking the Democratic nomination for governor,tweeted Tuesday night:When I sat at the negotiation table, nothing about my gender or genetics held me back. THIS is why we need more women in state government.

Morton did not return a call seeking comment Wednesday.

Politico reported that during the meeting board members were reviewing areport on gender wage gaps among students who graduated from the university system in 2015.The report, which looked at what students did after graduation and how much theyre earning, found that female graduates from various fieldshave an annual median salary of $37,000, which is $5,500 less than the median salary of male graduates. African American graduates make even less, with an annual median wage of $35,600.

[Here are the facts behind that 79 cent pay gap factoid]

Femalegraduates make less than men even though they account fornearly 60 percent of the graduating class, according to the report.Blacks, Hispanics and whites make up 12 percent, 25 percent and 52 percent of the graduating class, respectively.

During the meeting, Morton said that the wage gap will in some way be self-correcting because the university system has more female graduates than men, according to Politico.

The report also found significant discrepancies in pay among men and women who graduated with the same degrees.The median salaries of women with degrees in biological sciences, business and marketing, communication and journalism, security and protective services, social sciences, and visual and performing arts are from$1,200to $4,400 lower than those of men with similar credentials.The gap among agriculture, liberal arts and physical sciences graduates is even greater from $6,400to $9,400.

Yet the report also found that women with degrees in education, engineering, health professions and psychology make from$500 to$3,100 more than their male counterparts annually.

A history of the long fight for gender wage equality. (Daron Taylor/The Washington Post)

Florida is among more than a dozen states with equal pay laws that haveloopholes that allow employers to continue to pay women less, according to the American Association of University Women.Two states, Alabama and Mississippi, have no equal paylaws. And only a handful California, Illinois, Minnesota, Vermont, Massachusetts and Maryland have strong equal pay laws.

Nationally, womens annual earnings are about 80 percent of what men make, according to a recent report by the association.

The report attributes the wage gap partly to differences in career choices and to the fact that parenting more often puts womens professional lives at a disadvantage than it does mens. Twenty-three percent of mothers left the workforce 10 years after graduation, while 17 percent worked part-time, according to the association. Those numbers among fathers were 1 percent and 2 percent, respectively.

Despite factors such as life choices and parenting, women facepay gaps at every education level and in nearly every line of work, the report said.


In the federal government, how likely is it that a woman will make more than a man?

The poor just dont want health care: Republican congressman faces backlash over comments

Nobody dies because they dont have access to health care, GOP lawmaker says. He got booed.

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A Florida higher-ed official said women’s genetics may be keeping … – Washington Post

Florida higher education official said women may earn less than men because of genetics – New York Daily News

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Thousands of horsemen may have swept into Bronze Age Europe, transforming the local population – Science Magazine

A Yamnaya skeleton from a grave in the Russian steppe, which was the homeland of men who migrated to Europe.

XVodolazx/Wikimedia Commons

By Ann GibbonsFeb. 21, 2017 , 12:00 PM

Call it an ancient thousand man march. Early Bronze Age men from the vast grasslands of the Eurasian steppe swept into Europe on horseback about 5000 years agoand may have left most women behind. This mostly male migration may have persisted for several generations, sending men into the arms of European women who interbred with them, and leaving a lasting impact on the genomes of living Europeans.

It looks like males migrating in war, with horses and wagons, says lead author and population geneticist Mattias Jakobsson of Uppsala University in Sweden.

Europeans are the descendants of at least three major migrations of prehistoric people. First, a group of hunter-gatherers arrived in Europe about 37,000 years ago. Then, farmers began migrating from Anatolia (a region including present-day Turkey) into Europe 9000 years ago, but they initially didnt intermingle much with the local hunter-gatherers because they brought their own families with them. Finally, 5000 to 4800 years ago, nomadic herders known as the Yamnaya swept into Europe. They were an early Bronze Age culture that came from the grasslands, or steppes, of modern-day Russia and Ukraine, bringing with them metallurgy and animal herding skills and, possibly,Proto-Indo-European, themysterious ancestral tonguefrom which all of todays 400 Indo-European languages spring. Theyimmediately interbred with local Europeans, who were descendants of both the farmers and hunter-gatherers. Within a few hundred years, the Yamnaya contributed to at least half of central Europeans genetic ancestry.

To find out why this migration of Yamnaya had such a big impact on European ancestry, researchers turned to genetic data from earlier studies of archaeological samples. They analyzed differences in DNA inherited by 20 ancient Europeans who lived just after the migration of Anatolian farmers (6000 to 4500 years ago) and 16 who lived just after the influx of Yamnaya (3000 to 1000 years ago). The team zeroed in on differences in the ratio of DNA inherited on their X chromosomes compared with the 22 chromosomes that do not determine sex, the so-called autosomes. This ratio can reveal the proportion of men and women in an ancestral population, because women carry two X chromosomes, whereas men have only one.

Europeans who were alive from before the Yamnaya migration inherited equal amounts of DNA from Anatolian farmers on their X chromosome and their autosomes, the team reports today in the Proceedings of the National Academy of Sciences. This means roughly equal numbers of men and women took part in the migration of Anatolian farmers into Europe.

But when the researchers looked at the DNA later Europeans inherited from the Yamnaya, they found that Bronze Age Europeans had far less Yamnaya DNA on their X than on their other chromosomes. Using a statistical method developed by graduate student Amy Goldberg in the lab of population geneticist Noah Rosenberg at Stanford University in Palo Alto, California, the team calculated that there were perhaps 10 men for every woman in the migration of Yamnaya men to Europe (with a range of five to 14 migrating men for every woman). That ratio is extremeeven more lopsided than the mostly male wave of Spanish conquistadores who came by ship to the Americas in the late 1500s, Goldberg says.

Such a skewed ratio raises red flags for some researchers, who warn it is notoriously difficult to estimate the ratio of men to women accurately in ancient populations. But if confirmed, one explanation is that the Yamnaya men were warriors who swept into Europe on horses or drove horse-drawn wagons; horses had been recently domesticated in the steppe and the wheel was a recent invention. They may have been more focused on warfare, with faster dispersal because of technological inventions says population geneticist Rasmus Nielsen of the University of California, Berkeley, who is not part of the study.

But warfare isnt the only explanation. The Yamnaya men could have been more attractive mates than European farmers because they had horses and new technologies, such as copper hammers that gave them an advantage, Goldberg says.

The finding that Yamnaya men migrated for many generations also suggests that all was not right back home in the steppe. It would imply a continuing strongly negative push factor within the steppes, such as chronic epidemics or diseases, says archaeologist David Anthony of Hartwick College in Oneonta, New York, who was not an author of the new study. Or, he says it could be the beginning of cultures that sent out bands of men to establish new politically aligned colonies in distant lands, as in later groups of Romans or Vikings.

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Thousands of horsemen may have swept into Bronze Age Europe, transforming the local population – Science Magazine

Genetic data show mainly men migrated from the Pontic steppe to … – Science Daily

Science Daily
Genetic data show mainly men migrated from the Pontic steppe to …
Science Daily
A new study, looking at the sex-specifically inherited X chromosome of prehistoric human remains, shows that hardly any women took part in the extensive …

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Genetic data show mainly men migrated from the Pontic steppe to … – Science Daily

Genetic basis for male baldness identified in large-scale study – Medical News Today

Although common, male baldness can have negative psychological effects and some studies have even linked it to a handful of serious illnesses. New research identifies the genetic variants involved in the condition, which could eventually enable researchers to predict a person’s chances of hair loss.

Male baldness – also referred to as androgenetic alopecia or male pattern baldness (MPB) – affects a significant number of people in the United States, as the condition accounts for over 95 percent of all hair loss in men.

According to the American Hair Loss Association, two thirds of U.S. adults will be affected by MPB to a certain degree by the age of 35, and around 85 percent of men will have experienced significant hair loss by the age of 50.

A lot of these men are seriously affected by the condition, which can have a negative effect on a person’s self-image, as well as on their interpersonal relationships.

Additionally, some genetic studies have even associated MPB with negative clinical outcomes such as prostate cancer and cardiovascular disease.

A new study – led by Saskia Hagenaars and David Hill of the University of Edinburgh in the United Kingdom – explores the genetic basis for the condition. The findings were published in the journal PLOS Genetics.

Scientists analyzed the genomic and health data of more than 52,000 men enrolled in the UK Biobank – an international health resource offering health information on more than 500,000 individuals.

The team located more than 250 independent genetic regions linked to severe hair loss.

The researchers split the 52,000 participants into two groups: a so-called discovery sample of 40,000 people and a target sample of 12,000 individuals. Based on the genetic variants that separated those with no hair loss from those with severe hair loss, the team designed an algorithm aimed to predict who would develop MPB.

The algorithmic baldness predictor is based on a genetic score, and although accurate predictions are still a long way off, the results of this study might soon enable researchers to identify subgroups of the population that are particularly prone to hair loss.

In the present study, researchers found that 14 percent of the participants with a submedian genetic score had severe MPB, and 39 percent had no hair loss. By contrast, 58 percent of those scoring in the top 10 percent on the polygenic score had moderate to severe MPB.

Co-lead author Saskia Hagenaars – a Ph.D. student at the University of Edinburgh’s Centre for Cognitive Aging and Cognitive Epidemiology – comments on the findings:

“We identified hundreds of new genetic signals,” Hagenaars says. “It was interesting to find that many of the genetics signals for male pattern baldness came from the X chromosome, which men inherit from their mothers.”

The study’s other lead author, Dr. David Hill, notes that the study did not collect data on the age of baldness onset, but only on hair loss pattern. However, he adds that, “we would expect to see an even stronger genetic signal if we were able to identify those with early-onset hair loss.”

To the authors’ knowledge, this is the largest genetic study of MPB to date.

The study’s principal investigator, Dr. Riccardo Marioni, from the University of Edinburgh’s Centre for Genomic and Experimental Medicine, explains the significance of the findings:

“We are still a long way from making an accurate prediction for an individual’s hair loss pattern. However, these results take us one step closer. The findings pave the way for an improved understanding of the genetic causes of hair loss.”

Learn how a drug promises robust new hair growth.

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Genetic basis for male baldness identified in large-scale study – Medical News Today

Genetic data show mainly men migrated from the Pontic steppe to Europe 5000 years ago – Phys.Org

February 21, 2017

A new study, looking at the sex-specifically inherited X chromosome of prehistoric human remains, shows that hardly any women took part in the extensive migration from the Pontic-Caspian Steppe approximately 5,000 years ago. The great migration that brought farming practices to Europe 4,000 years earlier, on the other hand, consisted of both women and men. The difference in sex bias suggests that different social and cultural processes drove the two migrations.

Genetic data suggest that modern European ancestry represents a mosaic of ancestral contributions from multiple waves of prehistoric migration events. Recent studies of genomic variation in prehistoric human remains have demonstrated that two mass migration events are particularly important to understanding European prehistory: the Neolithic spread of agriculture from Anatolia starting around 9,000 years ago, and migration from the Pontic-Caspian Steppe around 5,000 years ago. These migrations are coincident with large social, cultural, and linguistic changes, and each has been inferred to have replaced more than half of the contemporaneous gene pool of resident Central Europeans.

Dramatic events in human prehistory can be investigated using patterns of genetic variation among the people that lived in those times. In particular, studies of differing female and male demographic histories on the basis of ancient genomes can provide information about complexities of social structures and cultural interactions in prehistoric populations.

Researchers from Uppsala and Stanford University investigated the genetic ancestry on the sex-specifically inherited X chromosome and the autosomes in 20 early Neolithic and 16 Late Neolithic/Bronze Age human remains. Contrary to previous hypotheses suggesting patrilocality (social system in which a family resides near the man’s parents) of many agricultural populations, they found no evidence of sex-biased admixture during the migration that spread farming across Europe during the early Neolithic.

For later migrations from the Pontic steppe during the early Bronze Age, however, we find a dramatic male bias. There are simply too few X-chromosomes from the migrants, which points to around ten migrating males for every migrating female, says Mattias Jakobsson, professor of Genetics at the Department of Organismal Biology, Uppsala University.

The research group found evidence of ongoing, primarily male, migration from the steppe to central Europe over a period of multiple generations, with a level of sex bias that excludes a pulse migration during a single generation.

The contrasting patterns of sex-specific migration during these two migrations suggest a view of differing cultural histories in which the Neolithic transition was driven by mass migration of both males and females in roughly equal numbersperhaps whole familieswhereas the later Bronze Age migration and cultural shift were instead driven by male migration.

Explore further: Baltic hunter-gatherers began farming without influence of migration, ancient DNA suggests

More information: “Ancient X chromosomes reveal contrasting sex bias in Neolithic and Bronze Age Eurasian migrations,” PNAS, DOI: 10.1073/pnas.1616392114 ,

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A new study, looking at the sex-specifically inherited X chromosome of prehistoric human remains, shows that hardly any women took part in the extensive migration from the Pontic-Caspian Steppe approximately 5,000 years ago. …

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Genetic data show mainly men migrated from the Pontic steppe to Europe 5000 years ago – Phys.Org

Men inherit male pattern baldness from their mum’s side of the family … – Metro

It all comes from your X chromosome (Picture: Getty)

Getting a bit smooth up top? Judging on how you feel about it, your mum is the one you should be blaming /thanking.

Researchers at the University of Edinburgh have found that men inherit most of their baldness genes from their mums side of the family.

For what is the largest ever analysis of hair loss, scientists looked at the DNA of 52,000 men.

They identified almost 300 genes that could contribute to male pattern baldness most of which come from the X chromosome.

Saskia Hagenaars, who jointly led the research, said: We identified hundreds of new genetic signals.

It was interesting to find that many of the genetics signals for male pattern baldness came from the X chromosome, which men inherit from their mothers.

Before this research, published in PLOS Genetics, scientists had only identified a handful of genes related to baldness.

The studys principle investigator, Dr Riccardo Marioni, added: We are still a long way from making an accurate prediction for an individuals hair loss pattern.

However, these results take us one step closer.

The findings pave the way for an improved understanding of the genetic causes of hair loss.

More here:
Men inherit male pattern baldness from their mum’s side of the family … – Metro

Experts Are One Step Closer To Predicting A Man’s Risk For Hair Loss – Huffington Post

More than 200 new genetic markers linked with male pattern baldness have been identified, according to a new study from the United Kingdom.

The findings greatly increase the number of known genetic markers linked with baldness in men; a previous large study identified just eight such markers.

The researchers in the new study were also able to use their set of genetic markers to predict mens chances of severe hair loss, although the scientists noted that their results apply more to large populations of people than to any given individual.

We are still a long way from making an accurate prediction for an individuals hair-loss pattern. However, these results take us one step closer, study co-author Riccardo Marioni, of the University of Edinburghs Centre for Genomic and Experimental Medicine, said in a statement. The findings pave the way for an improved understanding of the genetic causes of hair loss, Marioni said. [5 Myths About the Male Body]

In the study, the researchers analyzed information from more than 52,000 men ages 40 to 69 years in the United Kingdom. Of these men, about 32 percent said they had no hair loss, 23 percent said they had slight hair loss, 27 percent said they had moderate hair loss and 18 percent said they had severe hair loss

The researchers then analyzed participants genomes, looking for genetic variations, known as single-nucleotide polymorphisms, or SNPs, that were linked with severe hair loss. That search revealed 287 genetic variations, located on more than 100 genes, that were linked with severe hair loss.

Many of the genetic variations were located on or near genes that have previously been linked with hair growth, hair graying or the biological structures involved in making hair, the researchers said.

Forty of the genetic variations were located on the X chromosome, which men inherit from their mothers, the researchers said. One of the genes on the X chromosome the gene for the androgen receptor, which binds to the hormone testosterone was strongly linked with severe hair loss. Previous studies have also pinpointed this gene as tied to male pattern baldness.

The researchers then created a formula, which resulted in a genetic risk score, to try to predict the chances of severe hair loss in the men. Among those men with a below-average score, 39 percent had no hair loss and 14 percent had severe hair loss. In contrast, among those with a high score that put them in the top 10 percent of those in the study, 58 percent had moderate-to-severe hair loss.

The researchers noted that in the study, they did not collect information on the age at which the men started losing their hair. The scientists said they would expect to see even stronger genetic associations with hair loss if they were able to include information about which men experienced early onset hair loss.

As more information from these participants becomes available, the researchers may be able to further refine their predictions, they said.

The study was published today (Feb. 14) in the journal PLOS Genetics.

Original article on Live Science.

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Experts Are One Step Closer To Predicting A Man’s Risk For Hair Loss – Huffington Post

Baldness linked to over 280 genes – BioNews

A new study has found over 280 genes associated with male-pattern baldness.

These genes could be used to predict a man’s chance of hair loss or possibly provide targets for drug development in the future.

The research, published in PLOS Genetics, is the largest genomic study of baldness to date. Researchers studied the DNA of more than 52,000 men aged between 4069 years old enrolled in the UK Biobank, looking for genes associated with baldness.

‘We identified hundreds of new genetic signals,’ Saskia Hagenaars, a PhD student at the University of Edinburgh and co-lead author, said. ‘It was interesting to find that many of the genetics signals for male-pattern baldness came from the X chromosome, which men inherit from their mothers.’

Many of the 287 genes linked with hair loss were related to hair growth and development. The researchers used these genes to try to predict the chance that a man will go bald, and found that almost 60 percent of those with the most number of hair loss genes showed signs of moderate to serious balding. However, the authors state that predictions for individuals are still ‘relatively crude’.

‘Data were collected on hair-loss pattern but not age of onset; we would expect to see an even stronger genetic signal if we were able to identify those with early-onset hair loss,’ said Dr David Hill, University of Edinburgh, who co-led the research.

Male-pattern baldness affects around half of all men by the age of 50. The condition is hereditary and thought to be linked to levels of a certain male sex hormone. Previous genetic studies have also associated male-pattern baldness with prostate cancer and heart disease.

The study’s principal investigator, Dr Riccardo Marioniof theUniversity of Edinburgh, said: ‘We are still a long way from making an accurate prediction for an individual’s hair-loss pattern. However, these results take us one step closer. The findings pave the way for an improved understanding of the genetic causes of hair loss.’

The study was based on information from the first release of data from the UK Biobank in 2015. The authors say that the release of data from the full cohort will enable them to further refine their predictions of male-pattern baldness and investigate its genetic basis.

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Baldness linked to over 280 genes – BioNews

More Than 200 Baldness-Linked Genetic Markers Found – Yahoo News

More than 200 new genetic markers linked with male pattern baldness have been identified, according to a new study from the United Kingdom.

The findings greatly increase the number of known genetic markers linked with baldness in men; a previous large study identified just eight such markers.

The researchers in the new study were also able to use their set of genetic markers to predict men’s chances of severe hair loss, although the scientists noted that their results apply more to large populations of people than to any given individual.

“We are still a long way from making an accurate prediction for an individual’s hair-loss pattern. However, these results take us one step closer,” study co-author Riccardo Marioni, of the University of Edinburgh’s Centre for Genomic and Experimental Medicine, said in a statement. “The findings pave the way for an improved understanding of the genetic causes of hair loss,” Marioni said. [5 Myths About the Male Body]

In the study, the researchers analyzed information from more than 52,000 men ages 40 to 69 years in the United Kingdom. Of these men, about 32 percent said they had no hair loss, 23 percent said they had slight hair loss, 27 percent said they had moderate hair loss and 18 percent said they had severe hair loss

The researchers then analyzed participants’ genomes, looking for genetic variations, known as single-nucleotide polymorphisms, or SNPs, that were linked with severe hair loss. That search revealed 287 genetic variations, located on more than 100 genes, that were linked with severe hair loss.

Many of the genetic variations were located on or near genes that have previously been linked with hair growth, hair graying or the biological structures involved in making hair, the researchers said.

Forty of the genetic variations were located on the X chromosome, which men inherit from their mothers, the researchers said. One of the genes on the X chromosome the gene for the androgen receptor, which binds to the hormone testosterone was strongly linked with severe hair loss. Previous studies have also pinpointed this gene as tied to male pattern baldness.

The researchers then created a formula, which resulted in a genetic “risk score,” to try to predict the chances of severe hair loss in the men. Among those men with a below-average score, 39 percent had no hair loss and 14 percent had severe hair loss. In contrast, among those with a high score that put them in the top 10 percent of those in the study, 58 percent had moderate-to-severe hair loss.

The researchers noted that in the study, they did not collect information on the age at which the men started losing their hair. The scientists said they would expect to see even stronger genetic associations with hair loss if they were able to include information about which men experienced early onset hair loss.

As more information from these participants becomes available, the researchers may be able to further refine their predictions, they said.

The study was published today (Feb. 14) in the journal PLOS Genetics.

Original article on Live Science.

View post:
More Than 200 Baldness-Linked Genetic Markers Found – Yahoo News

Can Your Anxiety Impact How Long You Last In Bed? – Men’s Health

Men’s Health
Can Your Anxiety Impact How Long You Last In Bed?
Men’s Health
To rule out the influence of genetics, the researchers only studied male twins and brothers of twins. After analyzing their responses, the researchers found no link between anxiety symptoms reported in 2006 with later reports of premature ejaculation

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Can Your Anxiety Impact How Long You Last In Bed? – Men’s Health

Women in Data Science conference highlights female participation in male-dominated field – Daily Free Press (subscription)

Daily Free Press (subscription)
Women in Data Science conference highlights female participation in male-dominated field
Daily Free Press (subscription)
Later in the day, Caroline Uhler, a professor at MIT's Institute for Data, Systems, and Society, shared her research on weather forecasting models and her work with genetics. Audience members listened, taking notes on Uhler's data-driven research and

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Women in Data Science conference highlights female participation in male-dominated field – Daily Free Press (subscription)

Male Contraceptives Have A Messy History And A Bright Future – Yahoo News


Why is contraception the burden of women? Male contraception would seem to be a much easier way of having sex for fun and not sticking a woman with the baby, but its rarely been on the minds of scientists in the past. That may be about to change, especially with the recent success of Vasalgel in a clinical trial. But why did it take so long, and why is it going so slowly?

Currently contraception takes three forms when it comes to men: Withdrawal, vascetomy, or condoms. Pulling out requires experience and control, making it less than ideal for an act all about losing control. Vasectomy works, but is, well, a rather permanent solution most people dont want to resort to. And condoms generally work, and have the bonus of helping prevent STIs.

That said, contraceptive options for women tend to be riskier, healthwise. Hormonal birth control may, depending on your genetics, increase your risk of stroke, and other side effects of the pill, especially the psychological ones, had been downplayed or even covered up for years or decades. Tubal ligation is more dangerous than vasectomy, albeit only by a small margin, and also a permanent solution where one may not be wanted. And IUDs have rare, but potentially serious, risks. Simply put, biology makes it much easier for men to use contraceptives, but historically, its been the womans job.

The main issue is that where women produce one cell a month, men crank out literally over a thousand sperm per second. That makes male birth control inherently more hit-or-miss since, despite making millions of them, you only need one to get pregnant. And, it has to be said, theres also the social aspect: Men dont get pregnant, and its easier to simply stick the woman with the responsibility and walk away. The history of birth control is littered with ugly incidents where sex without babies was seen as more important than womens health.

That doesnt mean, however, that men havent been trying, and even succeeding to some degree. The ancient Greeks mixed hemp seeds and rue in alcohol to lower sperm count, a method which worked in rat studies conducted thousands of years later. Gossypol, a polymer found in cottonseed oil used for cooking, turned out to be effective, but had a high risk of permanent infertility. And recently, the folklore that papaya seeds reduce fertility turned out to be accurate.

The problem is that the fields had several high profile failures. For example, a few months ago, Facebook had a good giggle at the idea of fragile men unable to handle the side effects of an experimental set of hormonal birth control shots. But that ignored that as the study has scaled up, it had gotten more and more reports of excessively increased libido from more than a third of study participants and 20% reporting mood disorders. That meant one of two things: The drug was riskier than previously thought, or something in the trial had gone wrong.


There are, however, a host of other options. Calcium channel blockers, encouraging the immune system to attack sperm, and even an alpha blocker that simply prevents ejaculation are all out there and being tested. And noninvasive surgical options, like the aforementioned Vasalgel, which is already in human trials in India, and a treatment blasting the testicles with ultrasound to kill sperm, are also showing promise.

So whats the issue? Why is research so slow? In a word? Trust. Women have repeatedly expressed a discomfort in trusting men to be in charge of their reproductive destiny. In fact, it can even be a form of domestic violence: In 2010, 10% of men and 9% of women report theyve been the targets of reproductive coercion, in which someone is forced into a pregnancy by means of sabotaging their birth control, or being impregnated without their consent. And only recently have the courts viewed removing a condom during sex as a serious crime.

That, combined with the fears of some men that male birth control will make them less of a man, can be a difficult hurdle for some to jump. That said, men should be allowed to take more control of their reproductive destiny. And medical science finally seems ready to give them just that.

Excerpt from:
Male Contraceptives Have A Messy History And A Bright Future – Yahoo News

The impact of RABL2B gene (rs144944885) on human male infertility in patients with oligoasthenoteratozoospermia … – UroToday

Male infertility is a multifactorial disorder with impressively genetic basis; besides, sperm abnormalities are the cause of numerous cases of male infertility. In this study, we evaluated the genetic variants in exons 4 and 5 and their intron-exon boundaries in RABL2B gene in infertile men with oligoasthenoteratozoospermia (OAT) and immotile short tail sperm (ISTS) defects to define if there is any association between these variants and human male infertility.

To this purpose, DNA was extracted from peripheral blood and after PCR reaction and sequencing, the results of sequenced segments were analyzed. In the present study, 30 infertile men with ISTS defect and 30 oligoasthenoteratozoospermic infertile men were recruited. All men were of Iranian origin and it took 3years to collect patient’s samples with ISTS defect.

As a result, the 50776482 delC intronic variant (rs144944885) was identified in five patients with oligoasthenoteratozoospermia defect and one patient with ISTS defect in heterozygote form. This variant was not identified in controls. The allelic frequency of the 50776482 delC variant was significantly statistically higher in oligoasthenoteratozoospermic infertile men (p

According to the present study, 50776482 delC allele in the RABL2B gene could be a risk factor in Iranian infertile men with oligoasthenoteratozoospermia defect, but more genetic studies are required to understand the accurate role of this variant in pathogenesis of human male infertility.

Journal of assisted reproduction and genetics. 2017 Jan 30 [Epub ahead of print]

Seyedeh Hanieh Hosseini, Mohammad Ali Sadighi Gilani, Anahita Mohseni Meybodi, Marjan Sabbaghian

Department of Andrology, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran., Department of Genetics, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran., Department of Andrology, Reproductive Biomedicine Research Center, Royan Institute for Reproductive Biomedicine, ACECR, Tehran, Iran. .


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The impact of RABL2B gene (rs144944885) on human male infertility in patients with oligoasthenoteratozoospermia … – UroToday

Tortoiseshell cat – Wikipedia

Tortoiseshell is a cat coat coloring named for its similarity to tortoiseshell material. Tortoiseshell cats are almost exclusively female.[1][2][3] Male tortoiseshells are rare and are usually sterile.[4][a]

Also called torties for short, tortoiseshell cats combine two colors other than white, either closely mixed or in larger patches.[2] The colors are often described as red and black, but the “red” patches can instead be orange, yellow, or cream,[2] and the “black” can instead be chocolate, grey, tabby, or blue.[2] Tortoiseshell cats with the tabby pattern as one of their colors are sometimes referred to as a torbie.[6]

“Tortoiseshell” is typically reserved for particolored cats with relatively small or no white markings. Those that are largely white with tortoiseshell patches are described as tricolor,[2] tortoiseshell-and-white (in the United Kingdom), or calico (in Canada and the United States).[7]

Tortoiseshell markings appear in many different breeds, as well as in non-purebred domestic cats.[7] This pattern is especially preferred in the Japanese Bobtail breed,[8] and exists in the Cornish Rex group.[9]

Tortoiseshell cats have particolored coats with patches of various shades of red and black, and sometimes white. A tortoiseshell can also have splotches of orange or gold, but these colors are rarer on the breed.[4] The size of the patches can vary from a fine speckled pattern to large areas of color. Typically, the more white a cat has, the more solid the patches of color. Dilution genes may modify the coloring, lightening the fur to a mix of cream and blue, lilac or fawn; and the markings on tortoiseshell cats are usually asymmetrical.[10]

Occasionally tabby patterns of black and brown (eumelanistic) and red (phaeomelanistic) colors are also seen. These patched tabbies are often called a tortie-tabby, torbie or, with large white areas, a caliby.[10] Not uncommonly there will be a “split face” pattern with black on one side of the face and orange on the other, with a dividing line running down the bridge of the nose. Tortoiseshell coloring can also be expressed in the point pattern, referred to as a “tortie point”.[10]

Tortoiseshell and calico coats result from an interaction between genetic and developmental factors. The primary gene for coat color (B) for the colors brown, chocolate, cinnamon, etc., can be masked by the co-dominant gene for the orange color (O) which is on the X Chromosome and has two alleles, the orange (XO) and not-orange (Xo), that produce orange phaeomelanin and black eumelanin pigments, respectively. (NOTE: Typically, the X for the chromosome is assumed from context and the alleles are referred to by just the uppercase O for the orange, or lower case o for the not-orange.) The tortoiseshell and calico cats are indicated: Oo to indicate they are heterozygous on the O gene. The (B) and (O) genes can be further modified by a recessive dilute gene (dd) which softens the colors. Orange becomes cream, black becomes gray, etc. Various terms are used for specific colors, for example, gray is also called blue, orange is also called ginger. Therefore, a tortoiseshell cat may be a chocolate tortoiseshell or a blue/cream tortoiseshell or the like, based on the alleles for the (B) and (D) genes.

The cells of female cats, which like other mammalian females have two X chromosomes (XX), undergo the phenomenon of X-inactivation,[11][12] in which one or the other of the X-chromosomes is turned off at random in each cell in very early development. The inactivated X becomes a Barr body. Cells in which the chromosome carrying the orange (O) allele is inactivated express the alternative non-orange (o) allele, determined by the (B) gene. Cells in which the non-orange (o) allele is inactivated express the orange (O) allele. Pigment genes are expressed in melanocytes that migrate to the skin surface later in development. In bi-colored tortoiseshell cats, the melanocytes arrive relatively early, and the two cell types become intermingled, producing the characteristic brindled appearance consisting of an intimate mixture of orange and black cells, with occasional small diffuse spots of orange and black.

In tri-colored calico cats, a separate gene interacts developmentally with the coat color gene. This spotting gene produces white, unpigmented patches by delaying the migration of the melanocytes to the skin surface. There are a number of alleles of this gene that produce greater or lesser delays. The amount of white is artificially divided into mitted, bicolor, harlequin, and van, going from almost no white to almost completely white. In the extreme case, no melanocytes make it to the skin and the cat is entirely white (but not an albino). In intermediate cases, melanocyte migration is slowed, so that the pigment cells arrive late in development and have less time to intermingle. Observation of tri-color cats will show that, with a little white color, the orange and black patches become more defined, and with still more white, the patches become completely distinct. Each patch represents a clone of cells derived from one original cell in the early embryo.[13]

A male cat, like males of other therian mammals, has only one X and one Y chromosome (XY). That X chromosome does not undergo X-inactivation, and coat color is determined by which allele is present on the X. Accordingly, the cat’s coat will be either entirely orange or non-orange. Very rarely (approximately 1 in 3,000[14]) a male tortoiseshell or calico is born. These animals typically have an extra X chromosome (XXY), a condition known in humans as Klinefelter syndrome, and their cells undergo an X-inactivation process like that in females. As in humans, these cats often are sterile because of the imbalance in sex chromosomes. Some male calico or tortoiseshell cats may be chimeras, which result from the fusion in early development of two (fraternal twin) embryos with different color genotypes. Others are mosaics, in which the XXY condition arises after conception and the cat is a mixture of cells with different numbers of X chromosomes.

In the folklore of many cultures, cats of the tortoiseshell coloration are believed to bring good luck.[15] Dating back to Celtic times, tortoiseshell cats have been perceived to bring good fortune into their homes. Even today, the Irish and Scottish believe stray tortoiseshell cats bring them luck.[16] In the United States, tortoiseshells are sometimes referred to as money cats.[17]

One study found that tortoiseshell owners frequently believe their cats have increased attitude (“tortitude”);[18] however, little scientific evidence supports this.[19] According to celebrity cat expert Jackson Galaxy, tortoiseshell cats tend to have a much more distinct personality.[20]

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Tortoiseshell cat – Wikipedia

Entrepreneurship Is Genetic, And South Africa Is The Ideal Environment For Young Entrepreneurs To Thrive – Huffington Post South Africa (blog)

Knowing the real South Africa is to know, and be familiar with, the ambitious entrepreneurial spirit that runs through its tributaries and flows like a river into the heart of a nation. South Africans have always been opportunistic, from J.B.M Hertzog who founded Naspers, which is now Africa’s largest company and globally the 7th largest internet company, to MTN and Discovery, both of which can now be found all over the world. We can even highlight the contributions of one of the world’s most foremost thinkers and innovators, Elon Musk, the driving force behind SpaceX.

Recently, Ventureburn did an article on the Top Entrepreneurs Under 40 in South Africa, highlighting how this spirit continues to grow and is a far cry from fading anytime soon. But what differentiates the men and women who started these companies from those of us ‘normal’ people who would not regard ourselves as entrepreneurs?

Entrepreneurs are a rare breed of humans who choose to innovate and forge their ideas into successful business from the ground up. They’re fearless and believe that what they are creating is going to change the world forever. And guess what, research shows that this could be genetic.

A recent study at Kings College in London, headed up by Scott Shane, identified that 37 to 48 per cent of the tendency to be an entrepreneur is genetic, and that the tendency to identify new business opportunities is in your genes. If you take this study as anything to go by, then this is remarkable as genetics account for almost half of what is a determining factor in becoming an entrepreneur.

What we know about genetics is that in some cases almost half of who we are is genetic, or how we are made, and the rest is down to environmental factors (in other words, what we do and how we live). This presents us all with an incredible opportunity to take control of our environment to use our genetic strengths to reach our goal. For some, and I would encourage any young South African with ambition to consider this path, that goal is entrepreneurship.

Take the environment in South Africa, for instance. South Africa is still a young country that is constantly growing, discovering who it is, and where its place in the world will be. This is what makes it the ideal environment for those predisposed, by either genetics, environment or desire, to entrepreneurship to thrive. It’s not all dependent on your genotype, but a large proportion of it could be, according to this study, and this could be what drives certain people to tackle new, exciting business ventures that other people may be dissuaded from due to fear of failure and the unknown.

This isn’t the only study that associates entrepreneurship with being genetics.

Nicos Nicolaou is a researcher who has been heading up these new discoveries that attempt to link genetics to entrepreneurship. Although they still require more research, which will come as the science around the human genome develops, their findings are interesting. They explain that there is a “single nucleotide polymorphism (rs1486011) of the DRD3 gene on chromosome 3 to be significantly associated with the tendency to be an entrepreneur. This result is the first evidence of the association of a specific gene with entrepreneurship.”

Wouldn’t you like to know if you had this gene, especially if you can already be considered an entrepreneur? I know I would, as it would be interesting to discover if my genes influenced me to start DNAFit, or any of my other business ventures.

I would also like to know if this gene is related to not requiring as much sleep as the average person – entrepreneurs never rest while there is opportunity to innovate and expand our ideas!

Going even deeper, Zhang did twin studies to find out if personality and gender play a role in the development of entrepreneurship as well. Their study can be regarded as verging on epigenetic as it uses the environmental impact, as well as genes.

It is based on “1285 pairs of identical twins (449 male and 836 female pairs) and 849 pairs of same-sex fraternal twins (283 male and 566 female pairs), we found that females have a strong genetic influence and zero shared-environmental influences on their tendency to become entrepreneurs. In contrast, males show zero genetic influence, but a large shared-environmental influence… such individuals appear to be ‘both born and made’.”

The difference in gender also make clear the notion that genes influence females and males differently, but they still eventually reach the same conclusion on their journey. As with everything, we still do not know enough about our genes to get conclusive, definite answers, and, even then, never forget environmental effects could re-direct people in a variety of ways.

How much start-up capital are you able to attain? How dedicated is your work force to your vision so that make it a success? How well-received are you not only by the market but by the influential people who rely on to believe in your brand as well?

And those are just a few factors…

Studies like the ones above do show how genetics are becoming more important than ever before when it comes to our understanding of the world. It’s not only about predisposition to disease, ancestry, and race.

We are becoming more and more capable of harnessing the power of genetics and applying it to our daily lives, and there is an opportunity to make South Africa the best environment for entrepreneurship in the world. Take the example of other great startup cities, such as Lisbon. In Lisbon, they went to great lengths to provide great access to capital, human resource, and cut red-tape for new businesses. Now, Lisbon is one of the top startup cities in the world – nominated European Capital of Entrepreneurship in 2015.

In South Africa, we have the ability to follow Lisbon, and go even further. With a talented, ambitious, and abundant workforce, great access to high quality office space and a low cost of living, we have everything the country needs to be the next Silicon Valley. Coupled with our incredible quality of life (and weather!), it seems to me that for all South Africans, this a time where nothing should be holding you back.

It’s inspirational to think that our entrepreneurial fire has only been started, and we as a country should do everything we can to foster an environment supportive of entrepreneurship and startup culture for everybody no matter how or where they were born. With this approach, we can make South Africa a world leader in both our genetic talent pool, and our fostering environment for entrepreneurship.

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Entrepreneurship Is Genetic, And South Africa Is The Ideal Environment For Young Entrepreneurs To Thrive – Huffington Post South Africa (blog)

Binary thought suppresses identity – The Daily Evergreen

WSU forms ask non-inclusive race and gender questions, even though these answers are not important to the evaluation of the form.

While our country has become increasingly more accepting of individuality, there are still many instances where our society is failing to adequately represent minorities.

For example, the WSU Junior Writing Portfolios (JWP) cover sheet asks students to specify their gender as either male or female, giving no option for individuals who do not identify as one or the other.

Freshman mechanical engineering major Nicklaus McHendry said that they have had difficulties with how to identify themself for others.

Ive been out as a non-binary person for many years, McHendry said. At this point (it is exhausting to see) a question with a binary male or female box on a form that I dont particularly feel I need to be asked that on.

So, why is WSU asking questions such as these on forms where specifying something such as gender or race isnt necessary? For the JWP, WSU just wants a representation of a students writing ability.

I dont feel that my gender or anyone elses should be specified on a form that doesnt have anything to do with it, McHendry said.

The director of writing assessments, Xyanthe Neider, wrote in an email that students can mark the gender that they feel most adequately represents them or they can leave the question blank.

We understand that gender is much more fluid beyond the binary male/female designators and we revisit this regularly, Neider wrote.

However, there is no indication on the form to suggest that specifying ones gender is optional.

Consequently, attempting to answer this question has left many students confused and frustrated while they ponder which of the two boxes most correctly identifies them.

Its hard not to be upset, McHendry said. In order to get through the day and not spend every waking moment of my life being bothered, angry and upset … I try to focus on things that are more important.

If they want to ask about gender, they should add the option to write it in on the JWP form, which would make certain minority students feel more accepted.

In addition to the JWP, the WSU online application for admission requires students to report their gender as either male or female. The application also asks students to report their race.

Many universities across the country consider ethnicity and gender in the admission process, which unfairly puts some students at a disadvantage and gives others the upper hand.

According to, Washington is one of eight states that currently bans public universities from considering race in admissions, a policy known as Affirmative Action.

WSU does not discriminate on the basis of race, sex, sexual orientation, gender identity/expression (or) religion, the Office for Equal Opportunity states on its website.

It is completely inappropriate to ask students to specify certain personal demographics when those responses have absolutely nothing to do with the reason the form is completed.

So, if WSU is not allowed to consider race during the application process, then why are they asking students to specify it on their application?

Emily Hogan is a freshman genetics and cell biology major from Harrington, Delaware. She can be contacted at 335-2290 or The opinions expressed in this column are not necessarily those of the staff of The Daily Evergreen or those of The Office of Student Media.

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Binary thought suppresses identity – The Daily Evergreen

The 44 Chromosome Man | Understanding Genetics

In a recent article, a doctor in China has identified a man who has 44 chromosomes instead of the usual 46. Except for his different number of chromosomes, this man is perfectly normal in every measurable way.

His chromosomes are arranged in a stable way that could be passed on if he met a nice girl who had 44 chromosomes too. And this would certainly be possible in the future given his family history.

But why doesn’t he have any problems? A loss of one let alone two chromosomes is almost always fatal because so many essential genes are lost.

In this case, he has fewer chromosomes but is actually missing very few genes. Instead, he has two chromosomes stuck to two other chromosomes. More specifically, both his chromosome 14’s are stuck to his chromosome 15’s.

So he has almost all the same genes as any other person. He just has them packaged a bit differently.

This is an important finding because it tells us about a key genetic event in human prehistory. All the evidence points to humans, like their relatives the chimpanzees, having 48 chromosomes a million or so years ago. Nowadays most humans have 46.

What happened to this 44 chromosome man shows one way that the first step in this sort of change might have happened in our past. Scientists could certainly predict something like this. But now there is proof that it can actually happen.

Note added in Proof: Here are some older papers that I missed that have very similar findings:

And the current one:

Case Report: Potential Speciation in Humans Involving Robertsonian Translocations.

His Story

So how did this man end up with 44 chromosomes? It is a story of close relatives having children together. And a chromosomal rearrangement called a balanced translocation.

A balanced translocation is when one chromosome sticks to another. Because no genes are lost in this process, it usually doesn’t have any effect. Until these folks try to have kids that is.

Usually around 2/3 of pregnancies involving one person with a balanced translocation will end in miscarriage. This has to do with how chromosomes separate when eggs and sperm are made. This process is called meiosis.

Remember, humans (and most other living things) have two copies of each chromosome. So they have two copies of chromosome 1, two copies of chromosome 2, etc. Only one chromosome from each pair gets put into any one sperm or egg. That way, when the sperm fertilizes the egg, the fetus has the right number of chromosomes.

This is where the problem starts for people with a balanced translocation. They have one unpaired chromosome and a pair with an extra chromosome. Here is what can happen in this situation:

The top row represents two potential parents. The parent on the right has a balanced translocation. There are two possible ways for the fused chromosome to line up.

In the figure, only two chromosomes are shown. Numbers 14 and 15 were chosen because these are the two that are fused in the 44 chromosome man.

The parent with the balanced translocation can make 4 different kinds of sperm or egg (the second row). As the figure shows, when the eggs and sperm combine, 1/2 of the time the fetus ends up with an extra or missing chromosome. Unless this chromosome is the X, Y or number 21, the usual result is miscarriage or being born with severe problems.

In this case it would almost certainly result in miscarriage. In fact, the 44 chromosome man’s family has a long history of miscarriages and spontaneous abortions.

To get two of the same balanced translocations, both parents need to have the same balanced translocation. This is incredibly rare. Except when the parents are related.

In this case, both parents are first cousins and they share the same translocation. When these parents try to have kids, they run into the same kinds of problems that can happen with one balanced translocation. Except that the problems are doubled. This makes for the many possibilities outlined below:

This very complicated table shows the 36 possible outcomes when two parents with the same balanced translocation attempt to have a child.

In this representation, the father’s possible sperm are shown on the top and the mother’s eggs on the side. Each pregnancy has only an 8 in 36 chance for success. And 1 out of 36 would have two of the same balanced translocation (the circled possibility).

Theoretically the 44 chromosome man should have fewer problems having children than his parents did. As this figure shows, there are no unpaired chromosomes when he and a woman with 46 chromosomes have children. But all of their kids would have a balanced translocation:

So this is how he came to have 44 chromosomes. This might also be how humans started on the road to 46 chromosomes a million or so years ago.

See the article here:
The 44 Chromosome Man | Understanding Genetics

Sex – Wikipedia

Organisms of many species are specialized into male and female varieties, each known as a sex,[1] with some falling in between being intersex. Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent. Gametes can be identical in form and function (known as isogamy), but in many cases an asymmetry has evolved such that two sex-specific types of gametes (heterogametes) exist (known as anisogamy).

Among humans and other mammals, males typically carry XY chromosomes, whereas females typically carry XX chromosomes, which are a part of the XY sex-determination system. Other animals have a sex-determination system as well, such as the ZW sex-determination system in birds, and the X0 sex-determination system in insects.

The gametes produced by an organism are determined by its sex: males produce male gametes (spermatozoa, or sperm, in animals; pollen in plants) while females produce female gametes (ova, or egg cells); individual organisms which produce both male and female gametes are termed hermaphroditic. Frequently, physical differences are associated with the different sexes of an organism; these sexual dimorphisms can reflect the different reproductive pressures the sexes experience. For instance, mate choice and sexual selection can accelerate the evolution of physical differences between the sexes.











One of the basic properties of life is reproduction, the capacity to generate new individuals, and sex is an aspect of this process. Life has evolved from simple stages to more complex ones, and so have the reproduction mechanisms. Initially the reproduction was a replicating process that consists in producing new individuals that contain the same genetic information as the original or parent individual. This mode of reproduction is called asexual, and it is still used by many species, particularly unicellular, but it is also very common in multicellular organisms.[2] In sexual reproduction, the genetic material of the offspring comes from two different individuals. As sexual reproduction developed by way of a long process of evolution, intermediates exist. Bacteria, for instance, reproduce asexually, but undergo a process by which a part of the genetic material of an individual (donor) is transferred to an other (recipient).[3]

Disregarding intermediates, the basic distinction between asexual and sexual reproduction is the way in which the genetic material is processed. Typically, prior to an asexual division, a cell duplicates its genetic information content, and then divides. This process of cell division is called mitosis. In sexual reproduction, there are special kinds of cells that divide without prior duplication of its genetic material, in a process named meiosis. The resulting cells are called gametes, and contain only half the genetic material of the parent cells. These gametes are the cells that are prepared for the sexual reproduction of the organism.[4] Sex comprises the arrangements that enable sexual reproduction, and has evolved alongside the reproduction system, starting with similar gametes (isogamy) and progressing to systems that have different gamete types, such as those involving a large female gamete (ovum) and a small male gamete (sperm).[5]

In complex organisms, the sex organs are the parts that are involved in the production and exchange of gametes in sexual reproduction. Many species, particularly animals, have sexual specialization, and their populations are divided into male and female individuals. Conversely, there are also species in which there is no sexual specialization, and the same individuals both contain masculine and feminine reproductive organs, and they are called hermaphrodites. This is very frequent in plants.[6]

Sexual reproduction first probably evolved about a billion years ago within ancestral single-celled eukaryotes.[7] The reason for the evolution of sex, and the reason(s) it has survived to the present, are still matters of debate. Some of the many plausible theories include: that sex creates variation among offspring, sex helps in the spread of advantageous traits, that sex helps in the removal of disadvantageous traits, and that sex facilitates repair of germ-line DNA.

Sexual reproduction is a process specific to eukaryotes, organisms whose cells contain a nucleus and mitochondria. In addition to animals, plants, and fungi, other eukaryotes (e.g. the malaria parasite) also engage in sexual reproduction. Some bacteria use conjugation to transfer genetic material between cells; while not the same as sexual reproduction, this also results in the mixture of genetic traits.

The defining characteristic of sexual reproduction in eukaryotes is the difference between the gametes and the binary nature of fertilization. Multiplicity of gamete types within a species would still be considered a form of sexual reproduction. However, no third gamete is known in multicellular animals.[8][9][10]

While the evolution of sex dates to the prokaryote or early eukaryote stage,[11] the origin of chromosomal sex determination may have been fairly early in eukaryotes (see Evolution of anisogamy). The ZW sex-determination system is shared by birds, some fish and some crustaceans. XY sex determination is used by most mammals,[12] but also some insects,[13] and plants (Silene latifolia).[14]X0 sex-determination is found in certain insects.

No genes are shared between the avian ZW and mammal XY chromosomes,[15] and from a comparison between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in human, rather than X or Y, suggesting that the ZW and XY sex-determination systems do not share an origin, but that the sex chromosomes are derived from autosomal chromosomes of the common ancestor of birds and mammals. A paper from 2004 compared the chicken Z chromosome with platypus X chromosomes and suggested that the two systems are related.[16]

Sexual reproduction in eukaryotes is a process whereby organisms form offspring that combine genetic traits from both parents. Chromosomes are passed on from one generation to the next in this process. Each cell in the offspring has half the chromosomes of the mother and half of the father.[17] Genetic traits are contained within the deoxyribonucleic acid (DNA) of chromosomesby combining one of each type of chromosomes from each parent, an organism is formed containing a doubled set of chromosomes. This double-chromosome stage is called “diploid”, while the single-chromosome stage is “haploid”. Diploid organisms can, in turn, form haploid cells (gametes) that randomly contain one of each of the chromosome pairs, via meiosis.[18] Meiosis also involves a stage of chromosomal crossover, in which regions of DNA are exchanged between matched types of chromosomes, to form a new pair of mixed chromosomes. Crossing over and fertilization (the recombining of single sets of chromosomes to make a new diploid) result in the new organism containing a different set of genetic traits from either parent.

In many organisms, the haploid stage has been reduced to just gametes specialized to recombine and form a new diploid organism; in others, the gametes are capable of undergoing cell division to produce multicellular haploid organisms. In either case, gametes may be externally similar, particularly in size (isogamy), or may have evolved an asymmetry such that the gametes are different in size and other aspects (anisogamy).[19] By convention, the larger gamete (called an ovum, or egg cell) is considered female, while the smaller gamete (called a spermatozoon, or sperm cell) is considered male. An individual that produces exclusively large gametes is female, and one that produces exclusively small gametes is male. An individual that produces both types of gametes is a hermaphrodite; in some cases hermaphrodites are able to self-fertilize and produce offspring on their own, without a second organism.[20]

Most sexually reproducing animals spend their lives as diploid organisms, with the haploid stage reduced to single cell gametes.[21] The gametes of animals have male and female formsspermatozoa and egg cells. These gametes combine to form embryos which develop into a new organism.

The male gamete, a spermatozoon (produced within a testicle), is a small cell containing a single long flagellum which propels it.[22] Spermatozoa are extremely reduced cells, lacking many cellular components that would be necessary for embryonic development. They are specialized for motility, seeking out an egg cell and fusing with it in a process called fertilization.

Female gametes are egg cells (produced within ovaries), large immobile cells that contain the nutrients and cellular components necessary for a developing embryo.[23] Egg cells are often associated with other cells which support the development of the embryo, forming an egg. In mammals, the fertilized embryo instead develops within the female, receiving nutrition directly from its mother.

Animals are usually mobile and seek out a partner of the opposite sex for mating. Animals which live in the water can mate using external fertilization, where the eggs and sperm are released into and combine within the surrounding water.[24] Most animals that live outside of water, however, must transfer sperm from male to female to achieve internal fertilization.

In most birds, both excretion and reproduction is done through a single posterior opening, called the cloacamale and female birds touch cloaca to transfer sperm, a process called “cloacal kissing”.[25] In many other terrestrial animals, males use specialized sex organs to assist the transport of spermthese male sex organs are called intromittent organs. In humans and other mammals this male organ is the penis, which enters the female reproductive tract (called the vagina) to achieve inseminationa process called sexual intercourse. The penis contains a tube through which semen (a fluid containing sperm) travels. In female mammals the vagina connects with the uterus, an organ which directly supports the development of a fertilized embryo within (a process called gestation).

Because of their motility, animal sexual behavior can involve coercive sex. Traumatic insemination, for example, is used by some insect species to inseminate females through a wound in the abdominal cavitya process detrimental to the female’s health.

Like animals, plants have developed specialized male and female gametes.[26] Within seed plants, male gametes are contained within hard coats, forming pollen. The female gametes of plants are contained within ovules; once fertilized by pollen these form seeds which, like eggs, contain the nutrients necessary for the development of the embryonic plant.

Female (left) and male (right) cones are the sex organs of pines and other conifers.

Many plants have flowers and these are the sexual organs of those plants. Flowers are usually hermaphroditic, producing both male and female gametes. The female parts, in the center of a flower, are the pistils, each unit consisting of a carpel, a style and a stigma. One or more of these reproductive units may be merged to form a single compound pistil. Within the carpels are ovules which develop into seeds after fertilization. The male parts of the flower are the stamens: these consist of long filaments arranged between the pistil and the petals that produce pollen in anthers at their tips. When a pollen grain lands upon the stigma on top of a carpel’s style, it germinates to produce a pollen tube that grows down through the tissues of the style into the carpel, where it delivers male gamete nuclei to fertilize an ovule that eventually develops into a seed.

In pines and other conifers the sex organs are conifer cones and have male and female forms. The more familiar female cones are typically more durable, containing ovules within them. Male cones are smaller and produce pollen which is transported by wind to land in female cones. As with flowers, seeds form within the female cone after pollination.

Because plants are immobile, they depend upon passive methods for transporting pollen grains to other plants. Many plants, including conifers and grasses, produce lightweight pollen which is carried by wind to neighboring plants. Other plants have heavier, sticky pollen that is specialized for transportation by insects. The plants attract these insects or larger animals such as humming birds and bats with nectar-containing flowers. These animals transport the pollen as they move to other flowers, which also contain female reproductive organs, resulting in pollination.

Most fungi reproduce sexually, having both a haploid and diploid stage in their life cycles. These fungi are typically isogamous, lacking male and female specialization: haploid fungi grow into contact with each other and then fuse their cells. In some of these cases the fusion is asymmetric, and the cell which donates only a nucleus (and not accompanying cellular material) could arguably be considered “male”.[27]

Some fungi, including baker’s yeast, have mating types that create a duality similar to male and female roles. Yeast with the same mating type will not fuse with each other to form diploid cells, only with yeast carrying the other mating type.[28]

Fungi produce mushrooms as part of their sexual reproduction. Within the mushroom diploid cells are formed, later dividing into haploid sporesthe height of the mushroom aids the dispersal of these sexually produced offspring.

The most basic sexual system is one in which all organisms are hermaphrodites, producing both male and female gametes[citation needed] this is true of some animals (e.g. snails) and the majority of flowering plants.[29] In many cases, however, specialization of sex has evolved such that some organisms produce only male or only female gametes. The biological cause for an organism developing into one sex or the other is called sex determination.

In the majority of species with sex specialization, organisms are either male (producing only male gametes) or female (producing only female gametes). Exceptions are commonfor example, the roundworm C. elegans has an hermaphrodite and a male sex (a system called androdioecy).

Sometimes an organism’s development is intermediate between male and female, a condition called intersex. Sometimes intersex individuals are called “hermaphrodite”; but, unlike biological hermaphrodites, intersex individuals are unusual cases and are not typically fertile in both male and female aspects.

In genetic sex-determination systems, an organism’s sex is determined by the genome it inherits. Genetic sex-determination usually depends on asymmetrically inherited sex chromosomes which carry genetic features that influence development; sex may be determined either by the presence of a sex chromosome or by how many the organism has. Genetic sex-determination, because it is determined by chromosome assortment, usually results in a 1:1 ratio of male and female offspring.

Humans and other mammals have an XY sex-determination system: the Y chromosome carries factors responsible for triggering male development. The “default sex,” in the absence of a Y chromosome, is female-like. Thus, XX mammals are female and XY are male. In humans, biological sex is determined by five factors present at birth: the presence or absence of a Y chromosome (which alone determines the individual’s genetic sex), the type of gonads, the sex hormones, the internal reproductive anatomy (such as the uterus in females), and the external genitalia.[30]

XY sex determination is found in other organisms, including the common fruit fly and some plants.[29] In some cases, including in the fruit fly, it is the number of X chromosomes that determines sex rather than the presence of a Y chromosome (see below).

In birds, which have a ZW sex-determination system, the opposite is true: the W chromosome carries factors responsible for female development, and default development is male.[31] In this case ZZ individuals are male and ZW are female. The majority of butterflies and moths also have a ZW sex-determination system. In both XY and ZW sex determination systems, the sex chromosome carrying the critical factors is often significantly smaller, carrying little more than the genes necessary for triggering the development of a given sex.[32]

Many insects use a sex determination system based on the number of sex chromosomes. This is called X0 sex-determinationthe 0 indicates the absence of the sex chromosome. All other chromosomes in these organisms are diploid, but organisms may inherit one or two X chromosomes. In field crickets, for example, insects with a single X chromosome develop as male, while those with two develop as female.[33] In the nematode C. elegans most worms are self-fertilizing XX hermaphrodites, but occasionally abnormalities in chromosome inheritance regularly give rise to individuals with only one X chromosomethese X0 individuals are fertile males (and half their offspring are male).[34]

Other insects, including honey bees and ants, use a haplodiploid sex-determination system.[35] In this case diploid individuals are generally female, and haploid individuals (which develop from unfertilized eggs) are male. This sex-determination system results in highly biased sex ratios, as the sex of offspring is determined by fertilization rather than the assortment of chromosomes during meiosis.

For many species, sex is not determined by inherited traits, but instead by environmental factors experienced during development or later in life. Many reptiles have temperature-dependent sex determination: the temperature embryos experience during their development determines the sex of the organism. In some turtles, for example, males are produced at lower incubation temperatures than females; this difference in critical temperatures can be as little as 12C.

Many fish change sex over the course of their lifespan, a phenomenon called sequential hermaphroditism. In clownfish, smaller fish are male, and the dominant and largest fish in a group becomes female. In many wrasses the opposite is truemost fish are initially female and become male when they reach a certain size. Sequential hermaphrodites may produce both types of gametes over the course of their lifetime, but at any given point they are either female or male.

In some ferns the default sex is hermaphrodite, but ferns which grow in soil that has previously supported hermaphrodites are influenced by residual hormones to instead develop as male.[36]

Many animals and some plants have differences between the male and female sexes in size and appearance, a phenomenon called sexual dimorphism. Sex differences in humans include, generally, a larger size and more body hair in men; women have breasts, wider hips, and a higher body fat percentage. In other species, the differences may be more extreme, such as differences in coloration or bodyweight.

Sexual dimorphisms in animals are often associated with sexual selection the competition between individuals of one sex to mate with the opposite sex.[37] Antlers in male deer, for example, are used in combat between males to win reproductive access to female deer. In many cases the male of a species is larger than the female. Mammal species with extreme sexual size dimorphism tend to have highly polygynous mating systemspresumably due to selection for success in competition with other malessuch as the elephant seals. Other examples demonstrate that it is the preference of females that drive sexual dimorphism, such as in the case of the stalk-eyed fly.[38]

Other animals, including most insects and many fish, have larger females. This may be associated with the cost of producing egg cells, which requires more nutrition than producing spermlarger females are able to produce more eggs.[39] For example, female southern black widow spiders are typically twice as long as the males.[40] Occasionally this dimorphism is extreme, with males reduced to living as parasites dependent on the female, such as in the anglerfish. Some plant species also exhibit dimorphism in which the females are significantly larger than the males, such as in the moss Dicranum[41] and the liverwort Sphaerocarpos.[42] There is some evidence that, in these genera, the dimorphism may be tied to a sex chromosome,[42][43] or to chemical signalling from females.[44]

In birds, males often have a more colourful appearance and may have features (like the long tail of male peacocks) that would seem to put the organism at a disadvantage (e.g. bright colors would seem to make a bird more visible to predators). One proposed explanation for this is the handicap principle.[45] This hypothesis says that, by demonstrating he can survive with such handicaps, the male is advertising his genetic fitness to femalestraits that will benefit daughters as well, who will not be encumbered with such handicaps.

Read more:
Sex – Wikipedia

Breast CancerPatient Version – National Cancer Institute

The breast is made up of glands called lobules that can make milk and thin tubes called ducts that carry the milk from the lobules to the nipple. Breast tissue also contains fat and connective tissue, lymph nodes, and blood vessels.

The most common type of breast cancer is ductal carcinoma, which begins in the cells of the ducts. Breast cancer can also begin in the cells of the lobules and in other tissues in the breast. Ductal carcinoma in situ is a condition in which abnormal cells are found in the lining of the ducts but they haven’t spread outside the duct. Breast cancer that has spread from where it began in the ducts or lobules to surrounding tissue is called invasive breast cancer. In inflammatory breast cancer, the breast looks red and swollen and feels warm because the cancer cells block the lymph vessels in the skin.

In the U.S., breast cancer is the second most common cancer in women after skin cancer. It can occur in both men and women, but it is rare in men. Each year there are about 100 times more new cases of breast cancer in women than in men.

Key statistics about breast cancer from the SEER Cancer Statistics Review, 1975-2010.

Excerpt from:
Breast CancerPatient Version – National Cancer Institute

Drosophila melanogaster – Wikipedia

Drosophila melanogaster is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting with Charles W. Woodworth’s proposal of the use of this species as a model organism, D. melanogaster continues to be widely used for biological research in studies of genetics, physiology, microbial pathogenesis, and life history evolution. It is typically used because it is an animal species that is easy to care for, has four pairs of chromosomes, breeds quickly, and lays many eggs.[2]D. melanogaster is a common pest in homes, restaurants, and other occupied places where food is served.[3]

Flies belonging to the family Tephritidae are also called “fruit flies”. This can cause confusion, especially in Australia and South Africa, where the Mediterranean fruit fly Ceratitis capitata is an economic pest.

Wildtype fruit flies are yellow-brown, with brick-red eyes and transverse black rings across the abdomen. They exhibit sexual dimorphism: females are about 2.5 millimeters (0.098in) long; males are slightly smaller with darker backs. Males are easily distinguished from females based on colour differences, with a distinct black patch at the abdomen, less noticeable in recently emerged flies (see fig.), and the sexcombs (a row of dark bristles on the tarsus of the first leg). Furthermore, males have a cluster of spiky hairs (claspers) surrounding the reproducing parts used to attach to the female during mating. There are extensive images at FlyBase.[4]

Egg of D. melanogaster

The D. melanogaster lifespan is about 30 days at 29C (84F).

The developmental period for D. melanogaster varies with temperature, as with many ectothermic species. The shortest development time (egg to adult), 7 days, is achieved at 28C (82F).[5][6] Development times increase at higher temperatures (11 days at 30C or 86F) due to heat stress. Under ideal conditions, the development time at 25C (77F) is 8.5 days,[5][6][7] at 18C (64F) it takes 19 days[5][6] and at 12C (54F) it takes over 50 days.[5][6] Under crowded conditions, development time increases,[8] while the emerging flies are smaller.[8][9] Females lay some 400 eggs (embryos), about five at a time, into rotting fruit or other suitable material such as decaying mushrooms and sap fluxes. The eggs, which are about 0.5mm long, hatch after 1215 hours (at 25C or 77F).[5][6] The resulting larvae grow for about 4 days (at 25C) while molting twice (into second- and third-instar larvae), at about 24 and 48 h after hatching.[5][6] During this time, they feed on the microorganisms that decompose the fruit, as well as on the sugar of the fruit itself. The mother puts feces on the egg sacs to establish the same microbial composition in the larvae’s guts which has worked positively for herself.[10] Then the larvae encapsulate in the puparium and undergo a four-day-long metamorphosis (at 25C), after which the adults eclose (emerge).[5][6]

Females become receptive to courting males at about 812 hours after emergence.[11] Specific neuron groups in females have been found to affect copulation behavior and mate choice. One such group in the abdominal nerve cord allows the female fly to pause her body movements to copulate.[12] Activation of these neurons induces the female to cease movement and orient herself towards the male to allow for mounting. If the group is inactivated, the female remains in motion and does not copulate. Various chemical signals such as male pheromones often are able to activate the group.[12]

The female fruit fly prefers a shorter duration when it comes to sex. Males, on the other hand, prefer it to last longer.[13] Males perform a sequence of five behavioral patterns to court females. First, males orient themselves while playing a courtship song by horizontally extending and vibrating their wings. Soon after, the male positions itself at the rear of the female’s abdomen in a low posture to tap and lick the female genitalia. Finally, the male curls its abdomen and attempts copulation. Females can reject males by moving away, kicking, and extruding their ovipositor.[14] Copulation lasts around 1520 minutes,[15] during which males transfer a few hundred, very long (1.76mm) sperm cells in seminal fluid to the female.[16] Females store the sperm in a tubular receptacle and in two mushroom-shaped spermathecae; sperm from multiple matings compete for fertilization. A last male precedence is believed to exist in which the last male to mate with a female sires about 80% of her offspring. This precedence was found to occur through both displacement and incapacitation.[17] The displacement is attributed to sperm handling by the female fly as multiple matings are conducted and is most significant during the first 12 days after copulation. Displacement from the seminal receptacle is more significant than displacement from the spermathecae.[17] Incapacitation of first male sperm by second male sperm becomes significant 27 days after copulation. The seminal fluid of the second male is believed to be responsible for this incapacitation mechanism (without removal of first male sperm) which takes effect before fertilization occurs.[17] The delay in effectiveness of the incapacitation mechanism is believed to be a protective mechanism that prevents a male fly from incapacitating its own sperm should it mate with the same female fly repetitively. Sensory neurons in the uterus of female D. melanogaster respond to a male protein, sex peptide, which is found in sperm.[12] This protein makes the female reluctant to copulate for about 10 days after insemination. The signal pathway leading to this change in behavior has been determined. The signal is sent to a brain region that is a homolog of the hypothalamus and the hypothalamus then controls sexual behavior and desire[12]

D. melanogaster is often used for life extension studies, such as to identify genes purported to increase lifespan when mutated.[18]

D. melanogaster females exhibit mate choice copying. When virgin females are shown other females copulating with a certain type of male, they tend to copulate more with this type of male afterwards than naive females (which have not observed the copulation of others). This behavior is sensitive to environmental conditions, and females copy less in bad weather conditions.[19]

D. melanogaster males exhibit a strong reproductive learning curve. That is, with sexual experience, these flies tend to modify their future mating behavior in multiple ways. These changes include increased selectivity for courting only intraspecifically, as well as decreased courtship times.

Sexually nave D. melanogaster males are known to spend significant time courting interspecifically, such as with D. simulans flies. Nave D. melanogaster will also attempt to court females that are not yet sexually mature, and other males. D. melanogaster males show little to no preference for D. melanogaster females over females of other species or even other male flies. However, after D. simulans or other flies incapable of copulation have rejected the males advances, D. melanogaster males are much less likely to spend time courting nonspecifically in the future. This apparent learned behavior modification seems to be evolutionarily significant, as it allows the males to avoid investing energy into futile sexual encounters.[20]

In addition, males with previous sexual experience will modify their courtship dance when attempting to mate with new females the experienced males spend less time courting and therefore have lower mating latencies, meaning that they are able to reproduce more quickly. This decreased mating latency leads to a greater mating efficiency for experienced males over nave males.[21] This modification also appears to have obvious evolutionary advantages, as increased mating efficiency is extremely important in the eyes of natural selection.

Both male and female D. melanogaster act polygamously (having multiple sexual partners at the same time).[22] In both males and females, polygamy results in a decrease in evening activity compared to virgin flies, more so in males than females.[22] Evening activity consists of the activities that the flies participate in other than mating and finding partners, such as finding food.[23] The reproductive success of males and females varies, due to the fact that a female only needs to mate once to reach maximum fertility.[23] Mating with multiple partners provides no advantage over mating with one partner, and therefore females exhibit no difference in evening activity between polygamous and monogamous individuals.[23] For males, however, mating with multiple partners increases their reproductive success by increasing the genetic diversity of their offspring.[23] This benefit of genetic diversity is an evolutionary advantage because it increases the chance that some of the offspring will have traits that increase their fitness in their environment.

The difference in evening activity between polygamous and monogamous male flies can be explained with courtship. For polygamous flies, their reproductive success increases by having offspring with multiple partners, and therefore they spend more time and energy on courting multiple females.[23] On the other hand, monogamous flies only court one female, and expend less energy doing so.[23] While it requires more energy for male flies to court multiple females, the overall reproductive benefits it produces has kept polygamy as the preferred sexual choice.[23]

It has been shown that the mechanism that affects courtship behavior in Drosophila is controlled by the oscillator neurons DN1s and LNDs.[24] Oscillation of the DN1 neurons was found to be effected by socio-sexual interactions, and is connected to mating-related decrease of evening activity.[24]

D. melanogaster was among the first organisms used for genetic analysis, and today it is one of the most widely used and genetically best-known of all eukaryotic organisms. All organisms use common genetic systems; therefore, comprehending processes such as transcription and replication in fruit flies helps in understanding these processes in other eukaryotes, including humans.[25]

Thomas Hunt Morgan began using fruit flies in experimental studies of heredity at Columbia University in 1910 in a laboratory known as the Fly Room. The Fly Room was cramped with eight desks, each occupied by students and their experiments. They started off experiments using milk bottles to rear the fruit flies and handheld lenses for observing their traits. The lenses were later replaced by microscopes, which enhanced their observations. Morgan and his students eventually elucidated many basic principles of heredity, including sex-linked inheritance, epistasis, multiple alleles, and gene mapping.[25]

D. melanogaster is one of the most studied organisms in biological research, particularly in genetics and developmental biology. The several reasons include:

Genetic markers are commonly used in Drosophila research, for example within balancer chromosomes or P-element inserts, and most phenotypes are easily identifiable either with the naked eye or under a microscope. In the list of example common markers below, the allele symbol is followed by the name of the gene affected and a description of its phenotype. (Note: Recessive alleles are in lower case, while dominant alleles are capitalised.)

Drosophila genes are traditionally named after the phenotype they cause when mutated. For example, the absence of a particular gene in Drosophila will result in a mutant embryo that does not develop a heart. Scientists have thus called this gene tinman, named after the Oz character of the same name.[27] This system of nomenclature results in a wider range of gene names than in other organisms.

The genome of D. melanogaster (sequenced in 2000, and curated at the FlyBase database[26]) contains four pairs of chromosomes: an X/Y pair, and three autosomes labeled 2, 3, and 4. The fourth chromosome is so tiny, it is often ignored, aside from its important eyeless gene. The D. melanogaster sequenced genome of 139.5 million base pairs has been annotated[28] and contains around 15,682 genes according to Ensemble release 73. More than 60% of the genome appears to be functional non-protein-coding DNA[29] involved in gene expression control. Determination of sex in Drosophila occurs by the X:A ratio of X chromosomes to autosomes, not because of the presence of a Y chromosome as in human sex determination. Although the Y chromosome is entirely heterochromatic, it contains at least 16 genes, many of which are thought to have male-related functions.[30]

A March 2000 study by National Human Genome Research Institute comparing the fruit fly and human genome estimated that about 60% of genes are conserved between the two species.[31] About 75% of known human disease genes have a recognizable match in the genome of fruit flies,[32] and 50% of fly protein sequences have mammalian homologs. An online database called Homophila is available to search for human disease gene homologues in flies and vice versa.[33]Drosophila is being used as a genetic model for several human diseases including the neurodegenerative disorders Parkinson’s, Huntington’s, spinocerebellar ataxia and Alzheimer’s disease. The fly is also being used to study mechanisms underlying aging and oxidative stress, immunity, diabetes, and cancer, as well as drug abuse.

Embryogenesis in Drosophila has been extensively studied, as its small size, short generation time, and large brood size makes it ideal for genetic studies. It is also unique among model organisms in that cleavage occurs in a syncytium.

During oogenesis, cytoplasmic bridges called “ring canals” connect the forming oocyte to nurse cells. Nutrients and developmental control molecules move from the nurse cells into the oocyte. In the figure to the left, the forming oocyte can be seen to be covered by follicular support cells.

After fertilization of the oocyte, the early embryo (or syncytial embryo) undergoes rapid DNA replication and 13 nuclear divisions until about 5000 to 6000 nuclei accumulate in the unseparated cytoplasm of the embryo. By the end of the eighth division, most nuclei have migrated to the surface, surrounding the yolk sac (leaving behind only a few nuclei, which will become the yolk nuclei). After the 10th division, the pole cells form at the posterior end of the embryo, segregating the germ line from the syncytium. Finally, after the 13th division, cell membranes slowly invaginate, dividing the syncytium into individual somatic cells. Once this process is completed, gastrulation starts.[34]

Nuclear division in the early Drosophila embryo happens so quickly, no proper checkpoints exist, so mistakes may be made in division of the DNA. To get around this problem, the nuclei that have made a mistake detach from their centrosomes and fall into the centre of the embryo (yolk sac), which will not form part of the fly.

The gene network (transcriptional and protein interactions) governing the early development of the fruit fly embryo is one of the best understood gene networks to date, especially the patterning along the anteroposterior (AP) and dorsoventral (DV) axes (See under morphogenesis).[34]

The embryo undergoes well-characterized morphogenetic movements during gastrulation and early development, including germ-band extension, formation of several furrows, ventral invagination of the mesoderm, and posterior and anterior invagination of endoderm (gut), as well as extensive body segmentation until finally hatching from the surrounding cuticle into a first-instar larva.

During larval development, tissues known as imaginal discs grow inside the larva. Imaginal discs develop to form most structures of the adult body, such as the head, legs, wings, thorax, and genitalia. Cells of the imaginal disks are set aside during embryogenesis and continue to grow and divide during the larval stagesunlike most other cells of the larva, which have differentiated to perform specialized functions and grow without further cell division. At metamorphosis, the larva forms a pupa, inside which the larval tissues are reabsorbed and the imaginal tissues undergo extensive morphogenetic movements to form adult structures.

Drosophila flies have both X and Y chromosomes, as well as autosomes. Unlike humans, the Y chromosome does not confer maleness; rather, it encodes genes necessary for making sperm. Sex is instead determined by the ratio of X chromosomes to autosomes. Furthermore, each cell “decides” whether to be male or female independently of the rest of the organism, resulting in the occasional occurrence of gynandromorphs.

Three major genes are involved in determination of Drosophila sex. These are sex-lethal, sisterless, and deadpan. Deadpan is an autosomal gene which inhibits sex-lethal, while sisterless is carried on the X chromosome and inhibits the action of deadpan. An AAX cell has twice as much deadpan as sisterless, so sex-lethal will be inhibited, creating a male. However, an AAXX cell will produce enough sisterless to inhibit the action of deadpan, allowing the sex-lethal gene to be transcribed to create a female.

Later, control by deadpan and sisterless disappears and what becomes important is the form of the sex-lethal gene. A secondary promoter causes transcription in both males and females. Analysis of the cDNA has shown that different forms are expressed in males and females. Sex-lethal has been shown to affect the splicing of its own mRNA. In males, the third exon is included which encodes a stop codon, causing a truncated form to be produced. In the female version, the presence of sex-lethal causes this exon to be missed out; the other seven amino acids are produced as a full peptide chain, again giving a difference between males and females.[35]

Presence or absence of functional sex-lethal proteins now go on to affect the transcription of another protein known as doublesex. In the absence of sex-lethal, doublesex will have the fourth exon removed and be translated up to and including exon 6 (DSX-M[ale]), while in its presence the fourth exon which encodes a stop codon will produce a truncated version of the protein (DSX-F[emale]). DSX-F causes transcription of Yolk proteins 1 and 2 in somatic cells, which will be pumped into the oocyte on its production.

Unlike mammals, Drosophila flies only have innate immunity and lack an adaptive immune response. The D. melanogaster immune system can be divided into two responses: humoral and cell-mediated. The former is a systemic response mediated through the Toll and imd pathways, which are parallel systems for detecting microbes. The Toll pathway in Drosophila is known as the homologue of Toll-like pathways in mammals. Spatzle, a known ligand for the Toll pathway in flies, is produced in response to Gram-positive bacteria, parasites, and fungal infection. Upon infection, pro-Spatzle will be cleaved by protease SPE (Spatzle processing enzyme) to become active Spatzle, which then binds to the Toll receptor located on the cell surface (Fat body, hemocytes) and dimerise for activation of downstream NF-B signaling pathways. The imd pathway, though, is triggered by Gram-negative bacteria through soluble and surface receptors (PGRP-LE and LC, respectively). D. melanogaster has a “fat body”, which is thought to be homologous to the human liver. It is the primary secretory organ and produces antimicrobial peptides. These peptides are secreted into the hemolymph and bind infectious bacteria, killing them by forming pores in their cell walls. Years ago[when?] many drug companies wanted to purify these peptides and use them as antibiotics. Other than the fat body, hemocytes, the blood cells in Drosophila, are known as the homologue of mammalian monocyte/macrophages, possessing a significant role in immune responses. It is known from the literature that in response to immune challenge, hemocytes are able to secrete cytokines, for example Spatzle, to activate downstream signaling pathways in the fat body. However, the mechanism still remains unclear.

In 1971, Ron Konopka and Seymour Benzer published “Clock mutants of Drosophila melanogaster”, a paper describing the first mutations that affected an animal’s behavior. Wild-type flies show an activity rhythm with a frequency of about a day (24 hours). They found mutants with faster and slower rhythms, as well as broken rhythmsflies that move and rest in random spurts. Work over the following 30 years has shown that these mutations (and others like them) affect a group of genes and their products that comprise a biochemical or biological clock. This clock is found in a wide range of fly cells, but the clock-bearing cells that control activity are several dozen neurons in the fly’s central brain.

Since then, Benzer and others have used behavioral screens to isolate genes involved in vision, olfaction, audition, learning/memory, courtship, pain, and other processes, such as longevity.

The first learning and memory mutants (dunce, rutabaga, etc.) were isolated by William “Chip” Quinn while in Benzer’s lab, and were eventually shown to encode components of an intracellular signaling pathway involving cyclic AMP, protein kinase A, and a transcription factor known as CREB. These molecules were shown to be also involved in synaptic plasticity in Aplysia and mammals.[citation needed]

Male flies sing to the females during courtship using their wings to generate sound, and some of the genetics of sexual behavior have been characterized. In particular, the fruitless gene has several different splice forms, and male flies expressing female splice forms have female-like behavior and vice versa. The TRP channels nompC, nanchung, and inactive are expressed in sound-sensitive Johnston’s organ neurons and participate in the transduction of sound.[36][37]

Furthermore, Drosophila has been used in neuropharmacological research, including studies of cocaine and alcohol consumption. Models for Parkinson’s disease also exist for flies.[38]

Stereo images of the fly eye

The compound eye of the fruit fly contains 760 unit eyes or ommatidia, and are one of the most advanced among insects. Each ommatidium contains eight photoreceptor cells (R1-8), support cells, pigment cells, and a cornea. Wild-type flies have reddish pigment cells, which serve to absorb excess blue light so the fly is not blinded by ambient light.

Each photoreceptor cell consists of two main sections, the cell body and the rhabdomere. The cell body contains the nucleus, while the 100-m-long rhabdomere is made up of toothbrush-like stacks of membrane called microvilli. Each microvillus is 12 m in length and about 60 nm in diameter.[39] The membrane of the rhabdomere is packed with about 100 million rhodopsin molecules, the visual protein that absorbs light. The rest of the visual proteins are also tightly packed into the microvillar space, leaving little room for cytoplasm.

The photoreceptors in Drosophila express a variety of rhodopsin isoforms. The R1-R6 photoreceptor cells express rhodopsin1 (Rh1), which absorbs blue light (480nm). The R7 and R8 cells express a combination of either Rh3 or Rh4, which absorb UV light (345nm and 375nm), and Rh5 or Rh6, which absorb blue (437nm) and green (508nm) light, respectively. Each rhodopsin molecule consists of an opsin protein covalently linked to a carotenoid chromophore, 11-cis-3-hydroxyretinal.[40]

As in vertebrate vision, visual transduction in invertebrates occurs via a G protein-coupled pathway. However, in vertebrates, the G protein is transducin, while the G protein in invertebrates is Gq (dgq in Drosophila). When rhodopsin (Rh) absorbs a photon of light its chromophore, 11-cis-3-hydroxyretinal, is isomerized to all-trans-3-hydroxyretinal. Rh undergoes a conformational change into its active form, metarhodopsin. Metarhodopsin activates Gq, which in turn activates a phospholipase C (PLC) known as NorpA.[41]

PLC hydrolyzes phosphatidylinositol (4,5)-bisphosphate (PIP2), a phospholipid found in the cell membrane, into soluble inositol triphosphate (IP3) and diacylglycerol (DAG), which stays in the cell membrane. DAG or a derivative of DAG causes a calcium-selective ion channel known as transient receptor potential (TRP) to open and calcium and sodium flows into the cell. IP3 is thought to bind to IP3 receptors in the subrhabdomeric cisternae, an extension of the endoplasmic reticulum, and cause release of calcium, but this process does not seem to be essential for normal vision.[41]

Calcium binds to proteins such as calmodulin (CaM) and an eye-specific protein kinase C (PKC) known as InaC. These proteins interact with other proteins and have been shown to be necessary for shut off of the light response. In addition, proteins called arrestins bind metarhodopsin and prevent it from activating more Gq. A sodium-calcium exchanger known as CalX pumps the calcium out of the cell. It uses the inward sodium gradient to export calcium at a stoichiometry of 3 Na+/ 1 Ca++.[42]

TRP, InaC, and PLC form a signaling complex by binding a scaffolding protein called InaD. InaD contains five binding domains called PDZ domain proteins, which specifically bind the C termini of target proteins. Disruption of the complex by mutations in either the PDZ domains or the target proteins reduces the efficiency of signaling. For example, disruption of the interaction between InaC, the protein kinase C, and InaD results in a delay in inactivation of the light response.

Unlike vertebrate metarhodopsin, invertebrate metarhodopsin can be converted back into rhodopsin by absorbing a photon of orange light (580nm).

About two-thirds of the Drosophila brain is dedicated to visual processing.[43] Although the spatial resolution of their vision is significantly worse than that of humans, their temporal resolution is around 10 times better.

The wings of a fly are capable of beating up to 220 times per second.[citation needed] Flies fly via straight sequences of movement interspersed by rapid turns called saccades.[44] During these turns, a fly is able to rotate 90 in less than 50 milliseconds.[44]

Characteristics of Drosophila flight may be dominated by the viscosity of the air, rather than the inertia of the fly body, but the opposite case with inertia as the dominant force may occur.[44] However, subsequent work showed that while the viscous effects on the insect body during flight may be negligible, the aerodynamic forces on the wings themselves actually cause fruit flies’ turns to be damped viscously.[45]

Drosophila is commonly considered a pest due to its tendency to infest habitations and establishments where fruit is found; the flies may collect in homes, restaurants, stores, and other locations.[3] Removal of an infestation can be difficult, as larvae may continue to hatch in nearby fruit even as the adult population is eliminated.

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Drosophila melanogaster – Wikipedia

Quantitative genetics – Wikipedia

Quantitative genetics is a branch of population genetics that deals with phenotypes that vary continuously (in characters such as height or mass)as opposed to discretely identifiable phenotypes and gene-products (such as eye-colour, or the presence of a particular biochemical).

Both branches use the frequencies of different alleles of a gene in breeding populations (gamodemes), and combine them with concepts from simple Mendelian inheritance to analyze inheritance patterns across generations and descendant lines. While population genetics can focus on particular genes and their subsequent metabolic products, quantitative genetics focuses more on the outward phenotypes, and makes summaries only of the underlying genetics.

Due to the continuous distribution of phenotypic values, quantitative genetics must employ many other statistical methods (such as the effect size, the mean and the variance) to link phenotypes (attributes) to genotypes. Some phenotypes may be analyzed either as discrete categories or as continuous phenotypes, depending on the definition of cut-off points, or on the metric used to quantify them.[1]:2769 Mendel himself had to discuss this matter in his famous paper,[2] especially with respect to his peas attribute tall/dwarf, which actually was “length of stem”.[3][4] Analysis of quantitative trait loci, or QTL,[5][6][7] is a more recent addition to quantitative genetics, linking it more directly to molecular genetics.

In diploid organisms, the average genotypic “value” (locus value) may be defined by the allele “effect” together with a dominance effect, and also by how genes interact with genes at other loci (epistasis). The founder of quantitative genetics – Sir Ronald Fisher – perceived much of this when he proposed the first mathematics of this branch of genetics.[8]

Being a statistician, he defined the gene effects as deviations from a central valueenabling the use of statistical concepts such as mean and variance, which use this idea.[9] The central value he chose for the gene was the midpoint between the two opposing homozygotes at the one locus. The deviation from there to the “greater” homozygous genotype can be named “+a”; and therefore it is “-a” from that same midpoint to the “lesser” homozygote genotype. This is the “allele” effect mentioned above. The heterozygote deviation from the same midpoint can be named “d”, this being the “dominance” effect referred to above.[10] The diagram depicts the idea. However, in reality we measure phenotypes, and the figure also shows how observed phenotypes relate to the gene effects. Formal definitions of these effects recognize this phenotypic focus.[11][12] Epistasis has been approached statistically as interaction (i.e., inconsistencies),[13] but epigenetics suggests a new approach may be needed.

If 0a was known as “over-dominance”.[14]

Mendel’s pea attribute “length of stem” provides us with a good example.[3] Mendel stated that the tall true-breeding parents ranged from 67 feet in stem length (183 213cm), giving a median of 198cm (= P1). The short parents ranged from 0.75 – 1.25 feet in stem length (23 46cm), with a rounded median of 34cm (= P2). Their hybrid ranged from 67.5 feet in length (183229cm), with a median of 206cm (= F1). The mean of P1 and P2 is 116cm, this being the phenotypic value of the homozygotes midpoint (mp). The allele affect (a) is [P1-mp] = 82cm = -[P2-mp]. The dominance effect (d) is [F1-mp] = 90cm.[15] This historical example illustrates clearly how phenotype values and gene effects are linked.

To obtain means, variances and other statistics, both quantities and their occurrences are required. The gene effects (above) provide the framework for quantities: and the frequencies of the contrasting alleles in the fertilization gamete-pool provide the information on occurrences.

Commonly, the frequency of the allele causing “more” in the phenotype (including dominance) is given the symbol p, while the frequency of the contrasting allele is q. An initial assumption made when establishing the algebra was that the parental population was infinite and random mating, which was made simply to facilitate the derivation. The subsequent mathematical development also implied that the frequency distribution within the effective gamete-pool was uniform: there were no local perturbations where p and q varied. Looking at the diagrammatic analysis of sexual reproduction, this is the same as declaring that pP = pg = p; and similarly for q.[14] This mating system, dependent upon these assumptions, became known as “panmixia”.

Panmixia rarely actually occurs in nature,[16]:152180[17] as gamete distribution may be limited, for example by dispersal restrictions or by behaviour, or by chance sampling (those local perturbations mentioned above). It is well-known that there is a huge wastage of gametes in Nature, which is why the diagram depicts a potential gamete-pool separately to the actual gamete-pool. Only the latter sets the definitive frequencies for the zygotes: this is the true “gamodeme” (“gamo” refers to the gametes, and “deme” derives from Greek for “population”). But, under Fisher’s assumptions, the gamodeme can be effectively extended back to the potential gamete-pool, and even back to the parental base-population (the “source” population). The random sampling arising when small “actual” gamete-pools are sampled from a large “potential” gamete-pool is known as genetic drift, and is considered subsequently.

While panmixia may not be widely extant, the potential for it does occur, although it may be only ephemeral because of those local perturbations. It has been shown, for example, that the F2 derived from random fertilization of F1 individuals (an allogamous F2), following hybridization, is an origin of a new potentially panmictic population.[18][19] It has also been shown that if panmictic random fertilization occurred continually, it would maintain the same allele and genotype frequencies across each successive panmictic sexual generationthis being the Hardy Weinberg equilibrium.[13]:3439[20][21][22][23] However, as soon as genetic drift was initiated by local random sampling of gametes, the equilibrium would cease.

Male and female gametes within the actual fertilizing pool are considered usually to have the same frequencies for their corresponding alleles. (Exceptions have been considered.) This means that when p male gametes carrying the A allele randomly fertilize p female gametes carrying that same allele, the resulting zygote has genotype AA, and, under random fertilization, the combination occurs with a frequency of p x p (= p2). Similarly, the zygote aa occurs with a frequency of q2. Heterozygotes (Aa) can arise in two ways: when p male (A allele) randomly fertilize q female (a allele) gametes, and vice versa. The resulting frequency for the heterozygous zygotes is thus 2pq.[13]:32 Notice that such a population is never more than half heterozygous, this maximum occurring when p=q= 0.5.

In summary then, under random fertilization, the zygote (genotype) frequencies are the quadratic expansion of the gametic (allelic) frequencies: ( p + q ) 2 = p 2 + 2 p q + q 2 = 1 {textstyle (p+q)^{2}=p^{2}+2pq+q^{2}=1} . (The “=1” states that the frequencies are in fraction form, not percentages; and that there are no omissions within the framework proposed.)

Notice that “random fertilization” and “panmixia” are not synonyms.

Mendel’s pea experiments were constructed by establishing true-breeding parents with “opposite” phenotypes for each attribute.[3] This meant that each opposite parent was homozygous for its respective allele only. In our example, “tall vs dwarf”, the tall parent would be genotype TT with p = 1 (and q = 0); while the dwarf parent would be genotype tt with q = 1 (and p = 0). After controlled crossing, their hybrid is Tt, with p = q = . However, the frequency of this heterozygote = 1, because this is the F1 of an artificial cross: it has not arisen through random fertilization.[24] The F2 generation was produced by natural self-pollination of the F1 (with monitoring against insect contamination), resulting in p = q = being maintained. Such an F2 is said to be “autogamous”. However, the genotype frequencies (0.25 TT, 0.5 Tt, 0.25 tt) have arisen through a mating system very different from random fertilization, and therefore the use of the quadratic expansion has been avoided. The numerical values obtained were the same as those for random fertilization only because this is the special case of having originally crossed homozygous opposite parents.[25] We can notice that, because of the dominance of T- [frequency (0.25 + 0.5)] over tt [frequency 0.25], the 3:1 ratio is still obtained.

A cross such as Mendel’s, where true-breeding (largely homozygous) opposite parents are crossed in a controlled way to produce an F1, is a special case of hybrid structure. The F1 is often regarded as “entirely heterozygous” for the gene under consideration. However, this is an over-simplification and does not apply generallyfor example when individual parents are not homozygous, or when populations inter-hybridise to form hybrid swarms.[24] The general properties of intra-species hybrids (F1) and F2 (both “autogamous” and “allogamous”) are considered in a later section.

Having noticed that the pea is naturally self-pollinated, we cannot continue to use it as an example for illustrating random fertilization properties. Self-fertilization (“selfing”) is a major alternative to random fertilization, especially within Plants. Most of the Earth’s cereals are naturally self-pollinated (rice, wheat, barley, for example), as well as the pulses. Considering the millions of individuals of each of these on Earth at any time, it’s obvious that self-fertilization is at least as significant as random fertilization. Self-fertilization is the most intensive form of inbreeding, which arises whenever there is restricted independence in the genetical origins of gametes. Such reduction in independence arises if parents are already related, and/or from genetic drift or other spatial restrictions on gamete dispersal. Path analysis demonstrates that these are tantamount to the same thing.[26][27] Arising from this background, the inbreeding coefficient (often symbolized as F or f) quantifies the effect of inbreeding from whatever cause. There are several formal definitions of f, and some of these are considered in later sections. For the present, note that for a long-term self-fertilized species f = 1. Natural self-fertilized populations are not single ” pure lines “, however, but mixtures of such lines. This becomes particularly obvious when considering more than one gene at a time. Therefore, allele frequencies (p and q) other than 1 or 0 are still relevant in these cases (refer back to the Mendel Cross section). The genotype frequencies take a different form, however.

In general, the genotype frequencies become [ p 2 ( 1 f ) + p f ] {textstyle [p^{2}(1-f)+pf]} for AA and 2 p q ( 1 f ) {textstyle 2pq(1-f)} for Aa and [ q 2 ( 1 f ) + q f ] {textstyle [q^{2}(1-f)+qf]} for aa.[13]:65

Notice that the frequency of the heterozygote declines in proportion to f. When f = 1, these three frequencies become respectively p, 0 and q Conversely, when f = 0, they reduce to the random-fertilization quadratic expansion shown previously.

The population mean shifts the central reference point from the homozygote midpoint (mp) to the mean of a sexually reproduced population. This is important not only to relocate the focus into the natural world, but also to use a measure of central tendency used by Statistics/Biometrics. In particular, the square of this mean is the Correction Factor, which is used to obtain the genotypic variances later.[9]

For each genotype in turn, its allele effect is multiplied by its genotype frequency; and the products are accumulated across all genotypes in the model. Some algebraic simplification usually follows to reach a succinct result.

The contribution of AA is p 2 ( + ) a {textstyle p^{2}(+)a} , that of Aa is 2 p q d {textstyle 2pqd} , and that of aa is q 2 ( ) a {textstyle q^{2}(-)a} . Gathering together the two a terms and accumulating over all, the result is: a ( p 2 q 2 ) + 2 p q d {textstyle a(p^{2}-q^{2})+2pqd} . Simplification is achieved by noting that ( p 2 q 2 ) = ( p q ) ( p + q ) {textstyle (p^{2}-q^{2})=(p-q)(p+q)} , and by recalling that ( p + q ) = 1 {textstyle (p+q)=1} , thereby reducing the right-hand term to ( p q ) {textstyle (p-q)} .

The succinct result is therefore G = a ( p q ) + 2 p q d {textstyle G=a(p-q)+2pqd} .[14]:110

This defines the population mean as an “offset” from the homozygote midpoint (recall a and d are defined as deviations from that midpoint). The Figure depicts G across all values of p for several values of d, including one case of slight over-dominance. Notice that G is often negative, thereby emphasizing that it is itself a deviation (from mp).

Finally, to obtain the actual Population Mean in “phenotypic space”, the midpoint value is added to this offset: P = G + m p {textstyle P=G+mp} .

An example arises from data on ear length in maize.[28]:103 Assuming for now that one gene only is represented, a = 5.45cm, d = 0.12cm [virtually “0”, really], mp = 12.05cm. Further assuming that p = 0.6 and q = 0.4 in this example population, then:

G = 5.45 (0.6 – 0.4) + (0.48)0.12 = 1.15cm (rounded); and

P = 1.15 + 12.05 = 13.20cm (rounded).

The contribution of AA is p ( + a ) {textstyle p(+a)} , while that of aa is q ( a ) {textstyle q(-a)} . [See above for the frequencies.] Gathering these two a terms together leads to an immediately very simple final result:

G ( f = 1 ) = a ( p q ) {textstyle G_{(f=1)}=a(p-q)} . As before, P = G + m p {textstyle P=G+mp} .

Often, “G(f=1)” is abbreviated to “G1”.

Mendel’s peas can provide us with the allele effects and midpoint (see previously); and a mixed self-pollinated population with p = 0.6 and q = 0.4 provides example frequencies. Thus:

G(f=1) = 82 (0.6 – .04) = 59.6cm (rounded); and

P(f=1) = 59.6 + 116 = 175.6cm (rounded).

A general formula incorporates the inbreeding coefficient f, and can then accommodate any situation. The procedure is exactly the same as before, using the weighted genotype frequencies given earlier. After translation into our symbols, and further rearrangement:[13]:7778

G f = a ( q p ) + [ 2 p q d f ( 2 p q d ) ] = a ( p q ) + ( 1 f ) 2 p q d = G 0 f 2 p q d {displaystyle {begin{aligned}G_{f}&=a(q-p)+[2pqd-f(2pqd)]\&=a(p-q)+(1-f)2pqd\&=G_{0}-f 2pqdend{aligned}}}

Supposing that the maize example [given earlier] had been constrained on a holme (a narrow riparian meadow), and had partial inbreeding to the extent of f = 0.25, then, using the third version (above) of Gf:

G0.25 = 1.15 – 0.25 (0.48) 0.12 = 1.136 cm (rounded), with P0.25 = 13.194 cm (rounded).

There is hardly any effect from inbreeding in this example, which arises because there was virtually no dominance in this attribute (d 0). Examination of all three versions of Gf reveals that this would lead to trivial change in the Population mean. Where dominance was notable, however, there would be considerable change.

Genetic drift was introduced when discussing the likelihood of panmixia being widely extant as a natural fertilization pattern. [See section on Allele and Genotype frequencies.] Here the sampling of gametes from the potential gamodeme is discussed in more detail. The sampling involves random fertilization between pairs of random gametes, each of which may contain either an A or an a allele. The sampling is therefore binomial sampling.[13]:382395[14]:4963[29]:35[30]:55 Each sampling “packet” involves 2N alleles, and produces N zygotes (a “progeny” or a “line”) as a result. During the course of the reproductive period, this sampling is repeated over and over, so that the final result is a mixture of sample progenies. The result is dispersed random fertilization ( ) {displaystyle left(bigodot right)} These events, and the overall end-result, are examined here with an illustrative example.

The “base” allele frequencies of the example are those of the potential gamodeme: the frequency of A is pg = 0.75, while the frequency of a is qg = 0.25. [White label “1” in the diagram.] Five example actual gamodemes are binomially sampled out of this base (s = the number of samples = 5), and each sample is designated with an “index” k: with k = 1 …. s sequentially. (These are the sampling “packets” referred to in the previous paragraph.) The number of gametes involved in fertilization varies from sample to sample, and is given as 2Nk [at white label “2” in the diagram]. The total () number of gametes sampled overall is 52 [white label “3” in the diagram]. Because each sample has its own size, weights are needed to obtain averages (and other statistics) when obtaining the overall results. These are k = 2 N k / ( k s 2 N k ) {textstyle omega _{k}=2N_{k}/(sum _{k}^{s}2N_{k})} , and are given at white label “4” in the diagram.

Following completion of these five binomial sampling events, the resultant actual gamodemes each contained different allele frequencies(pk and qk). [These are given at white label “5” in the diagram.] This outcome is actually the genetic drift itself. Notice that two samples (k = 1 and 5) happen to have the same frequencies as the base (potential) gamodeme. Another (k = 3) happens to have the p and q “reversed”. Sample (k = 2) happens to be an “extreme” case, with pk = 0.9 and qk = 0.1; while the remaining sample (k = 4) is “middle of the range” in its allele frequencies. All of these results have arisen only by “chance”, through binomial sampling. Having occurred, however, they set in place all the downstream properties of the progenies.

Because sampling involves chance, the probabilities ( k ) of obtaining each of these samples become of interest. These binomial probabilities depend on the starting frequencies (pg and qg) and the sample size (2Nk). They are tedious to obtain,[13]:382395[30]:55 but are of considerable interest. [See white label “6” in the diagram.] The two samples (k = 1, 5), with the allele frequencies the same as in the potential gamodeme, had higher “chances” of occurring than the other samples. Their binomial probabilities did differ, however, because of their different sample sizes (2Nk). The “reversal” sample (k = 3) had a very low Probability of occurring, confirming perhaps what might be expected. The “extreme” allele frequency gamodeme (k = 2) was not “rare”, however; and the “middle of the range” sample (k=4) was rare. These same Probabilities apply also to the progeny of these fertilizations.

Here, some summarizing can begin. The overall allele frequencies in the progenies bulk are supplied by weighted averages of the appropriate frequencies of the individual samples. That is: p = k s k p k {textstyle p_{centerdot }=sum _{k}^{s}omega _{k} p_{k}} and q = k s k q k {textstyle q_{centerdot }=sum _{k}^{s}omega _{k} q_{k}} . (Notice that k is replaced by for the overall result – a common practice.)[9] The results for the example are p = 0.631 and q = 0.369 [black label “5” in the diagram]. These values are quite different to the starting ones (pg and qg) [white label “1”]. The sample allele frequencies also have variance as well as an average. This has been obtained using the sum of squares (SS) method [31] [See to the right of black label “5” in the diagram]. [Further discussion on this variance occurs in the section below on Extensive genetic drift.]

The genotype frequencies of the five sample progenies are obtained from the usual quadratic expansion of their respective allele frequencies (random fertilization). The results are given at the diagram’s white label “7” for the homozygotes, and at white label “8” for the heterozygotes. Re-arrangement in this manner prepares the way for monitoring inbreeding levels. This can be done either by examining the level of total homozygosis [(p2k + q2k) = (1 – 2pkqk)] , or by examining the level of heterozygosis (2pkqk), as they are complementary.[32] Notice that samples k= 1, 3, 5 all had the same level of heterozygosis, despite one being the “mirror image” of the others with respect to allele frequencies. The “extreme” allele-frequency case (k= 2) had the most homozygosis (least heterozygosis) of any sample. The “middle of the range” case (k= 4) had the least homozygosity (most heterozygosity): they were each equal at 0.50, in fact.

The overall summary can continue by obtaining the weighted average of the respective genotype frequencies for the progeny bulk. Thus, for AA, it is p 2 = k s k p k 2 {textstyle p_{centerdot }^{2}=sum _{k}^{s}omega _{k} p_{k}^{2}} , for Aa , it is 2 p q = k s k 2 p k q k {textstyle 2p_{centerdot }q_{centerdot }=sum _{k}^{s}omega _{k} 2p_{k}q_{k}} and for aa, it is q 2 = k s k q k 2 {textstyle q_{centerdot }^{2}=sum _{k}^{s}omega _{k} q_{k}^{2}} . The example results are given at black label “7” for the homozygotes, and at black label “8” for the heterozygote. Note that the heterozygosity mean is 0.3588, which the next section uses to examine inbreeding resulting from this genetic drift.

The next focus of interest is the dispersion itself, which refers to the “spreading apart” of the progenies’ population means. These are obtained as G k = a ( p k q k ) + 2 p k q k d {textstyle G_{k}=a(p_{k}-q_{k})+2p_{k}q_{k}d} [see section on the Population mean], for each sample progeny in turn, using the example gene effects given at white label “9” in the diagram. Then, each P k = G k + m p {textstyle P_{k}=G_{k}+mp} is obtained also [at white label “10” in the diagram]. Notice that the “best” line (k = 2) had the highest allele frequency for the “more” allele (A) (it also had the highest level of homozygosity). The worst progeny (k = 3) had the highest frequency for the “less” allele (a), which accounted for its poor performance. This “poor” line was less homozygous than the “best” line; and it shared the same level of homozygosity, in fact, as the two second-best lines (k = 1, 5). The progeny line with both the “more” and the “less” alleles present in equal frequency (k = 4) had a mean below the overall average (see next paragraph), and had the lowest level of homozygosity. These results reveal the fact that the alleles most prevalent in the “gene-pool” (also called the “germplasm”) determine performance, not the level of homozygosity per se. Binomial sampling alone effects this dispersion.

The overall summary can now be concluded by obtaining G = k s k G k {textstyle G_{centerdot }=sum _{k}^{s}omega _{k} G_{k}} and P = k s k P k {textstyle P_{centerdot }=sum _{k}^{s}omega _{k} P_{k}} . The example result for P is 36.94 (black label “10” in the diagram). This later is used to quantify inbreeding depression overall, from the gamete sampling. [See the next section.] However, recall that some “non-depressed” progeny means have been identified already (k = 1, 2, 5). This is an enigma of inbreeding – while there may be “depression” overall, there are usually superior lines among the gamodeme samplings.

Included in the overall summary were the averaqe allele frequencies in the mixture of progeny lines (p and q). These can now be used to construct a hypothetical panmictic equivalent.[13]:382395[14]:4963[29]:35 This can be regarded as a “reference” to assess the changes wrought by the gamete sampling. The example appends such a panmictic to the right of the Diagram. The frequency of AA is therefore (p)2 = 0.3979. This is less than that found in the dispersed bulk (0.4513 at black label “7”). Similarly, for aa, (q)2 = 0.1303 – again less than the equivalent in the progenies bulk (0.1898). Clearly, genetic drift has increased the overall level of homozygosis by the amount (0.6411 – 0.5342) = 0.1069. In a complementary approach, the heterozygosity could be used instead. The panmictic equivalent for Aa is 2 p q = 0.4658, which is higher than that in the sampled bulk (0.3588) [black label “8”]. The sampling has caused the heterozygosity to decrease by 0.1070, which differs trivially from the earlier estimate because of rounding errors.

The inbreeding coefficient (f) was introduced in the early section on Self Fertilization. Here, a formal definition of it is considered: f is the probability that two “same” alleles (that is A and A, or a and a), which fertilize together are of common ancestral origin – or (more formally) f is the probability that two homologous alleles are autozygous.[14][27] Consider any random gamete in the potential gamodeme that has its syngamy partner restricted by binomial sampling. The probability that that second gamete is homologous autozygous to the first is 1/(2N), the reciprocal of the gamodeme size. For the five example progenies, these quantities are 0.1, 0.0833, 0.1, 0.0833 and 0.125 respectively, and their weighted average is 0.0961. This is the inbreeding coefficient of the example progenies bulk, provided it is unbiased with respect to the full binomial distribution. An example based upon s = 5 is likely to be biased, however, when compared to an appropriate entire binomial distribution based upon the sample number (s) approaching infinity (s ). Another derived definition of f for the full Distribution is that f also equals the rise in homozygosity, which equals the fall in heterozygosity.[33] For the example, these frequency changes are 0.1069 and 0.1070, respectively. This result is different to the above, indicating that bias with respect to the full underlying distribution is present in the example. For the example itself, these latter values are the better ones to use, namely f = 0.10695.

The population mean of the equivalent panmictic is found as [a (p-q) + 2 pq d] + mp. Using the example gene effects (white label “9” in the diagram), this mean is P = {textstyle P_{centerdot }=} 37.87. The equivalent mean in the dispersed bulk is 36.94 (black label “10”), which is depressed by the amount 0.93. This is the inbreeding depression from this Genetic Drift. However, as noted previously, three progenies were not depressed (k = 1, 2, 5), and had means even greater than that of the panmictic equivalent. These are the lines a plant breeder looks for in a line selection programme.[34]

If the number of binomial samples is large (s ), then p pg and q qg. It might be queried whether panmixia would effectively re-appear under these circumstances. However, the sampling of allele frequencies has still occurred, with the result that 2p, q 0.[35] In fact, as s , the p , q 2 p g q g 2 N {textstyle sigma _{p, q}^{2}to {tfrac {p_{g}q_{g}}{2N}}} , which is the variance of the whole binomial distribution.[13]:382395[14]:4963 Furthermore, the “Wahlund equations” show that the progeny-bulk homozygote frequencies can be obtained as the sums of their respective average values (p2 or q2) plus 2p, q.[13]:382395 Likewise, the bulk heterozygote frequency is (2 p q) minus twice the 2p, q. The variance arising from the binomial sampling is conspicuously present. Thus, even when s , the progeny-bulk genotype frequencies still reveal increased homozygosis, and decreased heterozygosis, there is still dispersion of progeny means, and still inbreeding and inbreeding depression. That is, panmixia is not re-attained once lost because of genetic drift (binomial sampling). However, a new potential panmixia can be initiated via an allogamous F2 following hybridization.[36]

Previous discussion on genetic drift examined just one cycle (generation) of the process. When the sampling continues over successive generations, conspicuous changes occur in 2p, q and f. Furthermore, another “index” is needed to keep track of “time”: t = 1 …. y where y = the number of “years” (generations) considered. The methodology often is to add the current binomial increment ( = “de novo”) to what has occurred previously.[13] The entire Binomial Distribution is examined here. [There is no further benefit to be had from an abbreviated example.]

Earlier this variance ( 2p,q[35]) was seen to be:-

p , q 2 = p g q g / 2 N = p g q g ( 1 2 N ) = p g q g f = p g q g f when used in recursive equations {displaystyle {begin{aligned}sigma _{p,q}^{2}&=p_{g}q_{g} / 2N\&=p_{g}q_{g}left({frac {1}{2N}}right)\&=p_{g}q_{g} f\&=p_{g}q_{g} Delta f scriptstyle {text{when used in recursive equations}}end{aligned}}}

With the extension over time, this is also the result of the first cycle, and so is 1 2 {textstyle sigma _{1}^{2}} (for brevity). At cycle 2, this variance is generated yet again – this time becoming the de novo variance ( 2 {textstyle Delta sigma ^{2}} ) – and accumulates to what was present already – the “carry-over” variance. The second cycle variance ( 2 2 {textstyle sigma _{2}^{2}} ) is the weighted sum of these two components, the weights being 1 {textstyle 1} for the de novo and ( 1 1 2 N ) {textstyle left(1-{tfrac {1}{2N}}right)} = ( 1 f ) {textstyle left(1-Delta fright)} for the”carry-over”.


2 2 = ( 1 ) 2 + ( 1 f ) 1 2 {displaystyle sigma _{2}^{2}=left(1right) Delta sigma ^{2}+left(1-Delta fright)sigma _{1}^{2}}

( 1)

The extension to generalize to any time t , after considerable simplification, becomes:[13]:328-

t 2 = p g q g [ 1 ( 1 f ) t ] {displaystyle sigma _{t}^{2}=p_{g}q_{g}left[1-left(1-Delta fright)^{t}right]}

( 2)

Because it was this variation in allele frequencies that caused the “spreading apart” of the progenies’ means (dispersion), the change in 2t over the generations indicates the change in the level of the dispersion.

The method for examining the inbreeding coefficient is similar to that used for 2p,q. The same weights as before are used respectively for de novo f ( f ) [recall this is 1/(2N) ] and carry-over f. Therefore, f 2 = ( 1 ) f + ( 1 f ) f 1 {textstyle f_{2}=left(1right)Delta f+left(1-Delta fright)f_{1}} , which is similar to Equation (1) in the previous sub-section.

In general, after rearrangement,[13]

f t = f + ( 1 f ) f t 1 = f ( 1 f t 1 ) + f t 1 {displaystyle {begin{aligned}f_{t}&=Delta f+left(1-Delta fright)f_{t-1}\&=Delta fleft(1-f_{t-1}right)+f_{t-1}end{aligned}}}

Still further rearrangements of this general equation reveal some interesting relationships.

(A) After some simplification,[13] ( f t f t 1 ) = f ( 1 f t 1 ) = f t {textstyle left(f_{t}-f_{t-1}right)=Delta fleft(1-f_{t-1}right)=delta f_{t}} . The left-hand side is the difference between the current and previous levels of inbreeding: the change in inbreeding (ft). Notice, that this change in inbreeding (ft) is equal to the de novo inbreeding (f) only for the first cycle – when ft-1 is zero.

(B) An item of note is the (1-ft-1), which is an “index of non-inbreeding”. It is known as the panmictic index.[13][14] P t 1 = ( 1 f t 1 ) {textstyle P_{t-1}=left(1-f_{t-1}right)} .

(C) Further useful relationships emerge involving the panmictic index.[13][14]

f = f t P t 1 = 1 P t P t 1 {displaystyle {begin{aligned}Delta f&={frac {delta f_{t}}{P_{t-1}}}\&=1-{frac {P_{t}}{P_{t-1}}}end{aligned}}}

f t = 1 ( 1 1 f ) t ( 1 f 0 ) {displaystyle {begin{aligned}f_{t}&=1-left(1-1Delta fright)^{t}left(1-f_{0}right)end{aligned}}}

It is easy to overlook that random fertilization includes self-fertilization. Sewall Wright showed that a proportion 1/N of random fertilizations is actually self fertilization ( ) {displaystyle left(bigotimes right)} , with the remainder (N-1)/N being cross fertilization ( X ) {displaystyle left({mathsf {X}}right)} . Following path analysis and simplification, the new view random fertilization inbreeding was found to be: f t = f ( 1 + f t 1 ) + N 1 N f t 1 {textstyle f_{t}=Delta fleft(1+f_{t-1}right)+{tfrac {N-1}{N}}f_{t-1}} .[27][37] Upon further rearrangement, the earlier results from the binomial sampling were confirmed, along with some new arrangements. Two of these were potentially very useful, namely: (A) f t = f [ 1 + f t 1 ( 2 N 1 ) ] {textstyle f_{t}=Delta fleft[1+f_{t-1}left(2N-1right)right]} ; and (B) f t = f ( 1 f t 1 ) + f t 1 {textstyle f_{t}=Delta fleft(1-f_{t-1}right)+f_{t-1}} .

The recognition that selfing may intrinsically be a part of random fertilization leads to some issues about the use of the previous random fertilization ‘inbreeding coefficient’. Clearly, then, it is inappropriate for any species incapable of self fertilization, which includes plants with self-incompatibility mechanisms, dioecious plants, and bisexual animals. The equation of Wright was modified later to provide a version of random fertilization that involved only cross fertilization with no self fertilization. The proportion 1/N formerly due to selfing now defined the carry-over gene-drift inbreeding arising from the previous cycle. The new version is:[13]:166

f X t = f t 1 + f ( 1 + f t 2 2 f t 1 ) {displaystyle f_{{mathsf {X}}_{t}}=f_{t-1}+Delta fleft(1+f_{t-2}-2f_{t-1}right)}

The graphs to the right depict the differences between standard random fertilization RF, and random fertilization adjusted for “cross fertilization alone” CF. As can be seen, the issue is non-trivial for small gamodeme sample sizes.

It now is necessary to note that not only is “panmixia” not a synonym for “random fertilization”, but also that “random fertilization” is not a synonym for “cross fertilization”.

In the sub-section on the “The sample gamodemes – Genetic drift”, a series of gamete samplings was followed, an outcome of which was an increase in homozygosity at the expense of heterozygosity. From this viewpoint, the rise in homozygosity was due to the gamete samplings. Levels of homozygosity can be viewed also according to whether homozygotes arose allozygously or autozygously. Recall that autozygous alleles have the same allelic origin, the likelihood (frequency) of which is the inbreeding coefficient (f) by definition. The proportion arising allozygously is therefore (1-f). For the A-bearing gametes, which are present with a general frequency of p, the overall frequency of those that are autozygous is therefore (f p). Similarly, for a-bearing gametes, the autozygous frequency is (f q).[38] These two viewpoints regarding genotype frequencies must be connected to establish consistency.

Following firstly the auto/allo viewpoint, consider the allozygous component. This occurs with the frequency of (1-f), and the alleles unite according to the random fertilization quadratic expansion. Thus:

( 1 f ) [ p 0 + q 0 ] 2 = ( 1 f ) [ p 0 2 + q 0 2 ] + ( 1 f ) [ 2 p 0 q 0 ] {displaystyle left(1-fright)left[p_{0}+q_{0}right]^{2}=left(1-fright)left[p_{0}^{2}+q_{0}^{2}right]+left(1-fright)left[2p_{0}q_{0}right]}

Secondly, the sampling viewpoint is re-examined. Previously, it was noted that the decline in heterozygotes was f ( 2 p 0 q 0 ) {textstyle fleft(2p_{0}q_{0}right)} . This decline is distributed equally towards each homozygote; and is added to their basic random fertilization expectations. Therefore, the genotype frequencies are: ( p 0 2 + f p 0 q 0 ) {textstyle left(p_{0}^{2}+fp_{0}q_{0}right)} for the “AA” homozygote; ( q 0 2 + f p 0 q 0 ) {textstyle left(q_{0}^{2}+fp_{0}q_{0}right)} for the “aa” homozygote; and 2 p 0 q 0 f ( 2 p 0 q 0 ) {textstyle 2p_{0}q_{0}-fleft(2p_{0}q_{0}right)} for the heterozygote.

Thirdly, the consistency between the two previous viewpoints needs establishing. It is apparent at once [from the corresponding equations above] that the heterozygote frequency is the same in both viewpoints. However, such a straightforward result is not immediately apparent for the homozygotes. Begin by considering the AA homozygote’s final equation in the auto/allo paragraph above:- [ ( 1 f ) p 0 2 + f p 0 ] {textstyle left[left(1-fright)p_{0}^{2}+fp_{0}right]} . Expand the brackets, and follow by re-gathering [within the resultant] the two new terms with the common-factor f in them. The result is: p 0 2 f ( p 0 2 p 0 ) {textstyle p_{0}^{2}-fleft(p_{0}^{2}-p_{0}right)} . Next, for the parenthesized ” p20 “, a (1-q) is substituted for a p, the result becoming p 0 2 f [ p 0 ( 1 q 0 ) p 0 ] {textstyle p_{0}^{2}-fleft[p_{0}left(1-q_{0}right)-p_{0}right]} . Following that substitution, it is a straightforward matter of multiplying-out, simplifying and watching signs. The end result is p 0 2 + f p 0 q 0 {textstyle p_{0}^{2}+fp_{0}q_{0}} , which is exactly the result for AA in the sampling paragraph. The two viewpoints are therefore consistent for the AA homozygote. In a like manner, the consistency of the aa viewpoints can also be shown. The two viewpoints are consistent for all classes of genotypes.

In previous sections, dispersive random fertilization (genetic drift) has been considered comprehensively, and self-fertilization and hybridizing have been examined to varying degrees. The diagram to the left depicts the first two of these, along with another “spatially based” pattern: islands. This is a pattern of random fertilization featuring dispersed gamodemes, with the addition of “overlaps” in which non-dispersive random fertilization occurs. With the islands pattern, individual gamodeme sizes (2N) are observable, and overlaps (m) are minimal. This is one of Sewall Wright’s array of possibilities.[37] In addition to “spatially” based patterns of fertilization, there are others based on either “phenotypic” or “relationship” criteria. The phenotypic bases include assortative fertilization (between similar phenotypes) and disassortative fertilization (between opposite phenotypes). The relationship patterns include sib crossing, cousin crossing and backcrossingand are considered in a separate section. Self fertilization may be considered both from a spatial or relationship point of view.

The breeding population consists of s small dispersed random fertilization gamodemes of sample size 2 N k {textstyle 2N_{k}} ( k = 1 … s ) with ” overlaps ” of proportion m k {textstyle m_{k}} in which non-dispersive random fertilization occurs. The dispersive proportion is thus ( 1 m k ) {textstyle left(1-m_{k}right)} . The bulk population consists of weighted averages of sample sizes, allele and genotype frequencies and progeny means, as was done for genetic drift in an earlier section. However, each gamete sample size is reduced to allow for the overlaps, thus finding a 2 N k {textstyle 2N_{k}} effective for ( 1 m k ) {textstyle left(1-m_{k}right)} .

For brevity, the argument is followed further with the subscripts omitted. Recall that 1 2 N {textstyle {tfrac {1}{2N}}} is f {textstyle Delta f} in general. [Here, and following, the 2N refers to the previously defined sample size, not to any “islands adjusted” version.]

After simplification,[37]

i s l a n d s f = ( 1 m ) 2 2 N m 2 ( 2 N 1 ) {displaystyle ^{mathsf {islands}}Delta f={frac {left(1-mright)^{2}}{2N-m^{2}left(2N-1right)}}}

This f is also substituted into the previous inbreeding coefficient to obtain [37]

i s l a n d s f t = i s l a n d s f t + ( 1 i s l a n d s f t ) i s l a n d s f t 1 {displaystyle {^{mathsf {islands}}f_{t}}= {^{mathsf {islands}}Delta f_{t}}+left(1- {^{mathsf {islands}}Delta f_{t}}right) {^{mathsf {islands}}f_{t-1}}}

The effective overlap proportion can be obtained also,[37] as

m t = 1 [ 2 N i s l a n d s f t ( 2 N 1 ) i s l a n d s f t + 1 ] 1 2 {displaystyle m_{t}=1-left[{frac {2N {^{mathsf {islands}}Delta f_{t}}}{left(2N-1right) {^{mathsf {islands}}Delta f_{t}+1}}}right]^{tfrac {1}{2}}}

The graphs to the right show the inbreeding for a gamodeme size of 2N = 50 for ordinary dispersed random fertilization (RF) (m=0), and for four overlap levels ( m = 0.0625, 0.125, 0.25, 0.5 ) of islands random fertilization. There has indeed been reduction in the inbreeding resulting from the non-dispersed random fertilization in the overlaps. It is particularly notable as m 0.50. Sewall Wright suggested that this value should be the limit for the use of this approach.[37]

The gene-model examines the heredity pathway from the point of view of “inputs” (alleles/gametes) and “outputs” (genotypes/zygotes), with fertilization being the “process” converting one to the other. An alternative viewpoint concentrates on the “process” itself, and considers the zygote genotypes as arising from allele shuffling. In particular, it regards the results as if one allele had “substituted” for the other during the shuffle, together with a residual that deviates from this view. This formed an integral part of Fisher’s method,[8] in addition to his use of frequencies and effects to generate his genetical statistics.[14] A discursive derivation of the allele substitution alternative follows.[14]:113

Suppose that the usual random fertilization of gametes in a “base” gamodeme – consisting of p gametes (A) and q gametes (a) – is replaced by fertilization with a “flood” of gametes all containing a single allele (A or a, but not both). The zygotic results can be interpreted in terms of the “flood” allele having “substituted for” the alternative allele in the underlying “base” gamodeme. The diagram assists in following this viewpoint: the upper part pictures an A substitution, while the lower part shows an a substitution. (The diagram’s “RF allele” is the allele in the “base” gamodeme.)

Consider the upper part firstly. Because base A is present with a frequency of p, the substitute A fertilizes it with a frequency of p resulting in a zygote AA with an allele effect of a. Its contribution to the outcome, therefore, is the product ( p a ) {textstyle left(p aright)} . Similarly, when the substitute fertilizes base a (resulting in Aa with a frequency of q and heterozygote effect of d), the contribution is ( q d ) {textstyle left(q dright)} . The overall result of substitution by A is, therefore, ( p a + q d ) {textstyle left(p a+q dright)} . This is now oriented towards the population mean [see earlier section] by expressing it as a deviate from that mean: ( p a + q d ) G {textstyle left(p a+q dright)-G}

After some algebraic simplification, this becomes

A = q [ a + ( q p ) d ] {displaystyle beta _{A}=q left[a+left(q-pright)dright]}

A parallel reasoning can be applied to the lower part of the diagram, taking care with the differences in frequencies and gene effects. The result is the substitution effect of a, which is

a = p [ a + ( q p ) d ] {displaystyle beta _{a}=- pleft[a+left(q-pright)dright]}

= a + ( q p ) d {displaystyle beta =a+left(q-pright)d}

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Beefalo – Wikipedia

Beefalo, also referred to as cattalo or the American hybrid, are a fertile hybrid offspring of domestic cattle (Bos taurus), usually a male in managed breeding programs, and the American bison (Bison bison), usually a female in managed breeding programs.[1][2] The breed was created to combine the characteristics of both animals for beef production.

Beefalo are primarily cattle in genetics and appearance, with the breed association defining a full Beefalo as one with three-eighths (37.5%) bison genetics, while animals with higher percentages of bison genetics are called “bison hybrids”.

Accidental crosses were noticed as long ago as 1749 in the southern English colonies of North America. Beef and bison were first intentionally crossbred during the mid-19th century.

The first deliberate attempts to cross breed bison with cattle was made by Colonel Samuel Bedson, warden of Stoney Mountain Penitentiary, Winnipeg, in 1880. Bedson bought eight bison from a captive herd of James McKay and inter-bred them with Durham cattle. The hybrids raised by Bedson were described by naturalist Ernest Thompson Seton:[3]

The hybrid animal is [claimed] to be a great improvement on both of its progenitors, as it is more docile and a better milker than the Buffalo, but retains its hardihood, while the robe is finer, darker and more even, and the general shape of the animal is improved by the reduction of the hump and increased proportion of the hind-quarters.

After seeing thousands of cattle die in a Kansas blizzard in 1886, Charles “Buffalo” Jones, a co-founder of Garden City, Kansas, also worked to cross bison and cattle at a ranch near the future Grand Canyon National Park, with the hope the animals could survive the harsh winters.[4] He called the result “cattalo” in 1888.[5]Mossom Boyd of Bobcaygeon, Ontario first started the practice in Canada, publishing about some of his outcomes in the Journal of Heredity.[6] After his death in 1914, the Canadian government continued experiments in crossbreeding up to 1964, with little success. For example, in 1936 the Canadian government had successfully cross-bred only 30 cattalos.[7] Lawrence Boyd continues the crossbreeding work of his grandfather on a farm in Alberta.[citation needed]

It was found early on that crossing a male bison with a domestic cow would produce few offspring, but that crossing a domestic bull with a bison cow apparently solved the problem. The female offspring proved fertile, but rarely so for the males. Although the cattalo performed well, the mating problems meant the breeder had to maintain a herd of wild and difficult-to-handle bison cows.[citation needed]

In 1965, Jim Burnett of Montana produced a hybrid bull that was fertile. Soon after, Cory Skowronek of California formed the World Beefalo Association and began marketing the hybrids as a new breed. The new name, Beefalo, was meant to separate this hybrid from the problems associated with the old cattalo hybrids. The breed was eventually set at being genetically at least five-eighths Bos taurus and at most three-eighths Bison bison.

A United States Department of Agriculture study[citation needed] found Beefalo meat, like bison meat, to be lower in fat and cholesterol than standard beef cattle. The American Beefalo Association states that Beefalo are better able to tolerate cold and need less assistance calving than cattle, while retaining domestic cattle’s docile nature and fast growth rate. They damage rangeland less than cattle.[8] They also state that Beefalo meat contains 4 to 6% more protein and is more tender, flavorful, and nutritious than a standard steer.[8] Beefalo has significantly less calories, fat, and cholesterol, than beef cattle, chicken, and cod.[9]

The American Beefalo Association states that the “crossbreeds are hardier, are more economical (and less care-intensive) to nurture, and produce meat that’s superior to that of the common cow.”[8]

In 1983, the three main Beefalo registration groups reorganized under the American Beefalo World Registry. Until November 2008, there were two Beefalo associations, the American Beefalo World Registry[10] and American Beefalo International. These organizations jointly formed the American Beefalo Association, Inc., which currently operates as the registering body for Beefalo in the United States.[11]

Most current bison herds are genetically polluted or partly crossbred with cattle.[12][13][14][15] There are only four genetically unmixed American bison herds left, and only two that are also free of brucellosis, the Wind Cave bison herd that roams Wind Cave National Park, South Dakota; and the Henry Mountains herd in the Henry Mountains of Utah.[16] A herd on Catalina island, California is not genetically pure or self-sustaining.

Dr. Dirk Van Vuren, formerly of the University of Kansas, however, points out that “The bison today that carry cattle DNA look exactly like bison, function exactly like bison and in fact are bison. For conservation groups, the interest is that they are not totally pure.”[17]

The term “cattalo” is defined by United States law as a cross of bison and cattle which have a bison appearance;[18] in Canada, however, the term is used for hybrids of all degrees and appearance. In the U.S., cattalo are regulated as “exotic animals”, along with pure bison and deer.

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Beefalo – Wikipedia