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Archive for the ‘Female Genetics’ Category

Human Genetics – Mendelian Inheritance 5

for 1st YEAR STUDENTS X-LINKED INHERITANCE

hen the locus for a gene for a particular trait or disease lies on the X chromosome, the disease is said to be X-linked. The inheritance pattern for X-linked inheritance differs from autosomal inheritance only because the X chromosome has no homologous chromosome in the male, the male has an X and a Y chromosome. Very few genes have been discovered on the Y chromosome.

The inheritance pattern follows the pattern of segregation of the X and Y chromosomes in meiosis and fertilization. A male child always gets his X from one of his mother’s two X’s and his Y chromosome from his father. X-linked genes are never passed from father to son. A female child always gets the father’s X chromosome and one of the two X’s of the mother. An affected female must have an affected father. Males are always hemizygous for X linked traits, that is, they can never be heterozygoses or homozygotes. They are never carriers. A single dose of a mutant allele will produce a mutant phenotype in the male, whether the mutation is dominant or recessive. On the other hand, females must be either homozygous for the normal allele, heterozygous, or homozygous for the mutant allele, just as they are for autosomal loci.

When an X-linked gene is said to express dominant inheritance, it means that a single dose of the mutant allele will affect the phenotype of the female. A recessive X-linked gene requires two doses of the mutant allele to affect the female phenotype. The following are the hallmarks of X-linked dominant inheritance:

The following Punnett Squares explain the first three hallmarks of X-linked dominant inheritance. X represents the X chromosome with the normal allele, XA represents the X chromosome with the mutant dominant allele, and Y represents the Y chromosome. Note that the affected father never passes the trait to his sons but passes it to all of his daughters, since the heterozygote is affected for dominant traits. On the other hand, an affected female passes the disease to half of her daughters and half of her sons.

Males are usually more severely affected than females because in each affected female there is one normal allele producing a normal gene product and one mutant allele producing the non-functioning product, while in each affected male there is only the mutant allele with its non-functioning product and the Y chromosome, no normal gene product at all. Affected females are more prevalent in the general population because the female has two X chromosomes, either of which could carry the mutant allele, while the male only has one X chromosome as a target for the mutant allele. When the disease is no more deleterious in males than it is in females, females are about twice as likely to be affected as males. As shown in Pedigree 5 below, X-linked dominant inheritance has a unique heritability pattern.

The key for determining if a dominant trait is X-linked or autosomal is to look at the offspring of the mating of an affected male and a normal female. If the affected male has an affected son, then the disease is not X-linked. All of his daughters must also be affected if the disease is X-linked. In Pedigree 5, both of these conditions are met.

What happens when males are so severely affected that they can’t reproduce? Suppose they are so severely affected they never survive to term, then what happens? This is not uncommon in X-linked dominant diseases. There are no affected males to test for X-linked dominant inheritance to see if the produce all affected daughters and no affected sons. Pedigree 6 shows the effects of such a disease in a family. There are no affected males, only affected females, in the population. Living females outnumber living males two to one when the mother is affected. The ratio in the offspring of affected females is: 1 affected female: 1 normal female: 1 normal male.

You will note that in Pedigree 6 there have also been several spontaneous abortions in the offspring of affected females. Normally, in the general population of us normal couples, one in six recognized pregnancies results in a spontaneous abortion. Here the ratio is much higher. Presumably many of the spontaneous abortions shown in Pedigree 6 are males that would have been affected had they survived to term.

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Human Genetics – Mendelian Inheritance 5

Androgenetic alopecia – Genetics Home Reference

Androgenetic alopecia is a common form of hair loss in both men and women. In men, this condition is also known as male-pattern baldness. Hair is lost in a well-defined pattern, beginning above both temples. Over time, the hairline recedes to form a characteristic “M” shape. Hair also thins at the crown (near the top of the head), often progressing to partial or complete baldness.

The pattern of hair loss in women differs from male-pattern baldness. In women, the hair becomes thinner all over the head, and the hairline does not recede. Androgenetic alopecia in women rarely leads to total baldness.

Androgenetic alopecia in men has been associated with several other medical conditions including coronary heart disease and enlargement of the prostate. Additionally, prostate cancer, disorders of insulin resistance (such as diabetes and obesity), and high blood pressure (hypertension) have been related to androgenetic alopecia. In women, this form of hair loss is associated with an increased risk of polycystic ovary syndrome (PCOS). PCOS is characterized by a hormonal imbalance that can lead to irregular menstruation, acne, excess hair elsewhere on the body (hirsutism), and weight gain.

Androgenetic alopecia is a frequent cause of hair loss in both men and women. This form of hair loss affects an estimated 50 million men and 30 million women in the United States. Androgenetic alopecia can start as early as a person’s teens and risk increases with age; more than 50 percent of men over age 50 have some degree of hair loss. In women, hair loss is most likely after menopause.

A variety of genetic and environmental factors likely play a role in causing androgenetic alopecia. Although researchers are studying risk factors that may contribute to this condition, most of these factors remain unknown. Researchers have determined that this form of hair loss is related to hormones called androgens, particularly an androgen called dihydrotestosterone. Androgens are important for normal male sexual development before birth and during puberty. Androgens also have other important functions in both males and females, such as regulating hair growth and sex drive.

Hair growth begins under the skin in structures called follicles. Each strand of hair normally grows for 2 to 6 years, goes into a resting phase for several months, and then falls out. The cycle starts over when the follicle begins growing a new hair. Increased levels of androgens in hair follicles can lead to a shorter cycle of hair growth and the growth of shorter and thinner strands of hair. Additionally, there is a delay in the growth of new hair to replace strands that are shed.

Although researchers suspect that several genes play a role in androgenetic alopecia, variations in only one gene, AR, have been confirmed in scientific studies. The AR gene provides instructions for making a protein called an androgen receptor. Androgen receptors allow the body to respond appropriately to dihydrotestosterone and other androgens. Studies suggest that variations in the AR gene lead to increased activity of androgen receptors in hair follicles. It remains unclear, however, how these genetic changes increase the risk of hair loss in men and women with androgenetic alopecia.

Researchers continue to investigate the connection between androgenetic alopecia and other medical conditions, such as coronary heart disease and prostate cancer in men and polycystic ovary syndrome in women. They believe that some of these disorders may be associated with elevated androgen levels, which may help explain why they tend to occur with androgen-related hair loss. Other hormonal, environmental, and genetic factors that have not been identified also may be involved.

Read more about the AR gene.

The inheritance pattern of androgenetic alopecia is unclear because many genetic and environmental factors are likely to be involved. This condition tends to cluster in families, however, and having a close relative with patterned hair loss appears to be a risk factor for developing the condition.

You may find the following resources about androgenetic alopecia helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? in the Handbook.

See the article here:
Androgenetic alopecia – Genetics Home Reference

The Genetics of Calico Cats – Department of Biology

In mammals, sex is determined by two sex chromosomes, known as the X and the Y chromosomes. Genes located on either the X or the Y chromosome are known as “sex-linked” genes. Genes on any chromosomes other than the X or Y are known as autosomal genes. The Karyotype: A Visualization of the Chromosomes Normal female mammals have two X chromosomes. Normal males have one X and one Y chromosome. This can be seen in this human male karyotype: The X and Y chromosomes appear at the bottom right corner of the image. If this were a female, the two sex chromosomes would both be relatively larger X chromosomes. As you can see, compared to the X chromosome, the Y chromosome is small and carries fewer genes.

The exact genes carried on the X chromosome varies among species. In humans, for example, the gene coding for normal clotting factors and the gene coding for normal cone photoreceptor pigment are located on the X chromosome. Abnormal mutant forms of these genes can result in hemophilia (a potentially fatal disorder in which the blood fails to clot) in the former case, and red-green color blindness in the latter.

There are two possible (normal) male genotypes:

At a certain point in the embryonic development of every female mammal (including cats), one of the two X chromosomes in each cell inactivates by supercoiling into a structure known as a Barr Body. This irreversible process is known as Lyonization; it leaves only ONE active X chromosome in each cell of the female embryo. Only the alleles on the active (uncoiled) X chromosome are expressed.

Lyonization is random in each cell: there’s no way to predict which of the two X chromosomes will become inactivated. Hence, any given cell of a heterozygous female could end up as either of the following:

A heterozygous cat will be a patchwork of these two types of cells. Lyonization takes place relatively early in development, when the cat is still a blastula, and all the cells descended from a blastomere with a particular X chromosome inactivated as a Barr Body will also have the same Barr Body inactivated. That means that all the skin tissues that arise from a cell like the left one will express black fur, and all the skin tissue that arise from a cell like the right one will express orange fur. Hence:

Here’s an overview:

This is why calico cats are almost invariably female.

A calico cat is a tortoiseshell expressing an additional genetic condition known as piebalding. A piebald animal has patches of white (i.e., unpigmented) skin/fur. This is controlled by a different locus (S) than the black/orange fur colors.

The patches may be relatively large, or rather small and interwoven:

Larger patches may be caused by:

See more here:
The Genetics of Calico Cats – Department of Biology

Tortoiseshell cat – Wikipedia, the free encyclopedia

Tortoiseshell describes a coat coloring found almost exclusively in female cats,[1][2] so called because of the similarity to the tortoiseshell material. Also called Torties for short, these cats combine two colors other than white, either closely mixed or in large patches.[2] The colors are often described as red and black, but “red” can instead be orange, yellow, or cream[2] and “black” can instead be chocolate, grey, tabby, or blue.[2] A tortoiseshell cat with the tabby pattern as one of its colors is a Torbie.

“Tortoiseshell” is typically reserved for 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). Tortoiseshell markings appear in many different breeds as well as in non-purebred domestic cats.[3] This pattern is especially preferred in the Japanese Bobtail breed.[4]

Tortoiseshell cats have coats with patches of various shades of red and black, as well as white. 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. The markings on tortoiseshell cats are usually asymmetrical. Occasionally tabby patterns of black and brown (eumelanistic) and red (phaeomelanistic) colors are also seen. These patched tabbies are often called tortie-tabby, torbie or, with large white areas, caliby.[5] Tortoiseshell can also be expressed in the point pattern.

Frequently there will be a “split face” pattern with black on one side of the face and orange on the other, with the dividing line running down the bridge of the nose.

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,[6][7] 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.[8]

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[9]) 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 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.

Cats of this coloration are believed to bring good luck in the folklore of many cultures.[10] In the United States, these are sometimes referred to as money cats.[11]

According to cat expert Jackson Galaxy, tortoiseshell cats tend to have a much more distinct personality.[12] The magazine of the Smithsonian Institution has reported that studies suggest many tortoiseshell owners believe their cats have increased attitude and they call it “tortitude” but science does not support this.[13]

Continued here:
Tortoiseshell cat – Wikipedia, the free encyclopedia

Spectacular Genetic Anomaly Results in Butterflies with …

James K. Adams, Professor of Biology, Dalton State College

Andrew D. Warren, Yale Peabody Museum of Natural History

mybutterflybugs

mybutterflybugs

Kim Davis, Mike Stangeland, and Andrew Warren, Butterflies of America

In the realm of genetic anomalies found in living organisms perhaps none is more visually striking than bilateral gynandromorphism, a condition where an animal or insect contains both male and female characteristics, evenly split, right down the middle. While cases have been reported in lobsters, crabs and even in birds, it seems butterflies and moths lucked out with the visual splendor of having both male and female wings as a result of the anomaly. For those interested in the science, heres a bit from Elise over at IFLScience:

In insects the mechanism is fairly well understood. A fly with XX chromosomes will be a female. However, an embryo that loses a Y chromosome still develops into what looks like an adult male, although it will be sterile. Its thought that bilateral gynandromorphism occurs when two sperm enter an egg. One of those sperm fuses with the nucleus of the egg and a female insect develops. The other sperm develops without another set of chromosomes within the same egg. Both a male and a female insect develop within the same body.

Above are some great examples of bilateral gynandromorphism, but follow the links above and below for many more. (via Live Science, The Endless Airshow, Butterflies of America, IFLScience)

See related posts on Colossal about butterflies, genetics.

Link:
Spectacular Genetic Anomaly Results in Butterflies with …

Female Infertility Genetic Causes | RSC New Jersey

Many women are unable to conceive and deliver a healthy baby due to genetic factors. Sometimes this is due to an inherited chromosome abnormality. Other times it is because of a single-gene defect passed from parent to child.

In addition, if other women in your family have had problems conceiving due to premature menopause, endometriosis or other factors, you may be at increased risk of the same problems.

Chromosomally abnormal embryos have a low rate of implantation in the mothers uterus, often leading to miscarriages. If an abnormal embryo does implant, the pregnancy may still result in miscarriage or the birth of a baby with physical problems, developmental delay, or mental retardation.

There are several kinds of chromosome abnormalities:

Translocation is the most common of these. Although a parent who carries a translocation is frequently normal, his or her embryo may receive too much or too little genetic material, and a miscarriage often results.

Couples with specific chromosome defects may benefit from pre-implantation genetic diagnosis (PGD) in conjunction with in vitro fertilization (IVF).

Down syndrome is usually associated with advanced maternal age and is a common example of aneuploidy. Down syndrome is caused by having an extra number-21 chromosome (three instead of two). It is also referred to as trisomy 21.

More information about genetics and chromosomes is available at the Web page Genetics Made Simple.

More rare is the existence of an inherited genetic disease due to abnormal genes or mutations. Chromosome analysis of the parents blood identifies such an inherited genetic cause in less than 5 percent of couples.

Single-gene abnormalities are mutations caused by changes in the DNA sequence of a gene, which produce proteins that allow cells to work properly. Gene mutations alter the functioning of cells due to a lack of a protein.

Single-gene disorders usually indicate a family history of a specific genetic disease such as cystic fibrosis (CF) an incurable and fatal disease affecting the mucous glands of vital organs and Tay Sachs, also a fatal disorder, in which harmful quantities of a fatty substance build up in tissues and nerve cells in the brain.

Though generally rare, these diseases are usually devastating to a family. Fortunately, much progress has been made in detection through pre-implantation genetic diagnosis (PGD) in conjunction with in vitro fertilization (IVF).

Although a couple may otherwise have no fertility problems, IVF and PGD can work together to spare mother and father from heartache in cases where there is a known single-gene family history.

Learn more about Genetics

Read more here:
Female Infertility Genetic Causes | RSC New Jersey

Female Hereditary Hair Loss Treatment & Genetic Testing …

http://www.baumanmedical.com – Hair loss affects tens of millions of American women, but new diagnostic procedures, effective treatments and tracking methods are available.

LaserCap delivers an effective, clinical dose of laser therapy anywhere, anytime because it is the first cordless, rechargeable, portable laser that has 224 separate laser diodes (not LEDs) that fits conveniently under a standard baseball hat. Laser treatments with LaserCap are 30 minutes, every other day. 650nm wavelength, 5mW per laser diode. Laser therapy does not regrow dead hair follicles, but it makes weaker hair follicles produce thicker, stronger and longer hair fibers. All laser patients should be measured in three areas using a HairCheck(TM) Cross sectional hair bundle measurement tool.

Female Androgen Sensitivity Genetic Testing is performed to determine if a women is likely to experience severe female hereditary hair loss and predict a post-menopausal woman’s response to the off-label treatment finasteride (propecia). The female Androgen Sensitivity test is performed in minutes in the doctor’s office using a cheek swab.

For more information on LaserCap, visit http://www.lasercap.info

To learn more about Hair Restoration Physician, Dr. Alan J. Bauman, M.D. visit http://www.baumanmedical.com

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Female Hereditary Hair Loss Treatment & Genetic Testing …

The Female Form: Embrace Your Genetics and Find Beauty in …

The following is a guest post by Amber Larsen of Massage and Health by Amber Kim:

My body, my face, my features will never be repeated. How I look is not going to mimic the girl next to me in the gym. My body shape will not be the same as another female that I may be slightly jealous of because shes thinner than me. My ass is going to be bigger and there is nothing I can do about it.

My genetics did it.

It’s amazing – on average, most women will have about thirteen negative thoughts about their appearance per day. If you break it down, it means that every waking hour we think negatively about ourselves. I cant lie; I know I have done the same. My ass is too big, my abs stick out, my latissimus dorsi is getting a bit too big because my bras are cutting into my skin (CrossFit did it).

According to cognitive behavioral psychology, the self-hate is called withdrawal emotions. These emotions make us want to withdraw from situations or things that are linked to the emotions that are causing us to feel this way. Essentially, you can say you can be withdrawing from yourself. This can cause us to either make drastic decisions, such as not to eat, or do things that can do us harm, or do the opposite – not take care of ourselves because we ask whats the use? I hope in writing this it can shed some light as to why you body looks the way it does, and how to embrace that you are unique and to work with your genetics.

What exactly is genetics? Genetics is a wide domain, but in short it is the study of heredity, more specifically the characteristics we inherit from our parents. Our appearance, abilities, susceptibility to disease, and even life span is influenced by heredity. That is just skimming the surface of genetics, but an overall view is that your body shape and your abilities in the gym are inherited from your parents. So what does that say about my personal body? My lower half will always be bigger because it is inherited from my father side. My upper body will always be a wee bit smaller because its inherited from my mothers side. The bottom line is, ladies, I will never weigh 110 pounds. Its not in my genetics, and you know what? Im okay with that.

Many times the media portrays an ideal size for a woman, but you know what? For a healthy woman who eats correctly and exercises on a regular basis there is no ideal size. The reason is because genetically we are all different. There is nothing wrong with a woman who has a leaner, thinner body, because she may be genetically predisposed to having a leaner frame. There is also nothing wrong with a woman who tends to be stronger looking with a larger frame for the same reason. Both body images are different, but both are ideal based on each individual womans inherited genetics.

Is your view on your body slowly changing?

So take a good look at my body (yes this is more difficult for me then you think). This photo is from 2012 and this is me at 140 pounds. If you see, my body is a bit stocky, bulky, and (since I am 53) technically overweight. By the way, you can see some of my cellulite and, yes, I did throw away my scale! My abs stick out and so does my ass.

You can see my body is made up of mostly fast-twitch muscle fibers, or type II muscle fibers. My muscles are different in that they contain a higher number of glycolytic enzymes, which means my muscles do very well anaerobically. Also, my body can be viewed as a bit of a subtype of fast twitch muscles in that I am efficient in strength movements and halfway decent at aerobic movements (not the best though). My body is adaptable with endurance training, but it will not be my strongest area of fitness. Bottom line, the body you see is genetically predisposed to strength work.

Now, a slow-twitch body will not look exactly like this. A slow-twitch body will be leaner because the muscle fibers tend to be longer. These muscles contain larger amounts of mitochondria and higher concentrations of myoglobin than my own body. Again, slow twitch muscle tissue is an inherited trait.

I am not super skinny (as you can see above), but its important to realize that each body is unique and has strengths and weaknesses. Each body is beautiful in its own right, and its important for all of you to embrace what makes you an individual. There is no ideal weight or look for any woman. Women look different based off of their genetic make up, and thats truly a beautiful thing. Just think – no one will ever look exactly like you. And you have automatically inherited strengths that will help you in your fitness goals.

Embrace the person you are. I know it can be difficult to stop the negative self talk that your body does not look like the skinny Victorias Secret model, but you know what? Maybe you were never meant to look that way based off of your genetic heredity. Maybe you were meant to look strong and maybe you were built for strength, which is beautiful. Even if you are a leaner person who wishes to look stronger, well you can, even with a leaner frame, and you can also embrace that your body allows you to work efficiently aerobically based on your genetic make-up.

The image you have of your body should be positive. No one can be you, and no one can look exactly like you because you are genetically different. There is so much beauty in that. Embrace the genetic make up that make your body unique to those around you. I hope you will not be afraid to wear that bikini this summer or to workout without a shirt on. Your body is beautiful because its uniquely you.

This is my body. I have learned to embrace the body that allows me to do amazing things. I hope you will do the same.

Read more from the original source:
The Female Form: Embrace Your Genetics and Find Beauty in …

XY sex-determination system – Wikipedia, the free encyclopedia

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

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

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

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

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

Humans, as well as some other organisms, can have a chromosomal arrangement that is contrary to their phenotypic sex; for example, XX males or XY females (see androgen insensitivity syndrome). Additionally, an abnormal number of sex chromosomes (aneuploidy) may be present, such as Turner’s syndrome, in which a single X chromosome is present, and Klinefelter’s syndrome, in which two X chromosomes and a Y chromosome are present, XYY syndrome and XXYY syndrome.[1] Other less common chromosomal arrangements include: triple X syndrome, 48, XXXX, and 49, XXXXX.

XY system in mammals: Sex is determined by presence of Y. “Female” is the default sex; due to the absence of the Y.[2] In the 1930s, Alfred Jost determined that the presence of testosterone was required for Wolffian duct development in the male rabbit.[3]

SRY is an intronless sex-determining gene on the Y chromosome in the therians (placental mammals and marsupials).[4] Non-human mammals use several genes on the Y-chromosome. Not all male-specific genes are located on the Y-chromosome. Other species (including most Drosophila species) use the presence of two X chromosomes to determine femaleness. One X chromosome gives putative maleness. The presence of Y-chromosome genes is required for normal male development.

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

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

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XY sex-determination system – Wikipedia, the free encyclopedia

Sexual differentiation – Wikipedia, the free encyclopedia

Sexual differentiation

Differentiation of the male and female reproductive systems does not occur until the fetal period of development.

Sexual differentiation is the process of development of the differences between males and females from an undifferentiated zygote. As male and female individuals develop from zygotes into fetuses, into infants, children, adolescents, and eventually into adults, sex and gender differences at many levels develop: genes, chromosomes, gonads, hormones, anatomy, and psyche.

Sex differences range greatly and include physiologically differentiating. Sex-dichotomous differences are developments which are wholly characteristic of one sex only. Examples of sex-dichotomous differences include aspects of the sex-specific genital organs such as ovaries, a uterus or a phallic urethra. In contrast, sex-dimorphic differences are matters of degree (e.g., size of phallus). Some of these (e.g., stature, behaviors) are mainly statistical, with much overlap between male and female populations.

Nevertheless, even the sex-dichotomous differences are not absolute in the human population, and there are individuals who are exceptions (e.g., males with a uterus, or females with an XY karyotype), or who exhibit biological and/or behavioral characteristics of both sexes.

Sex differences may be induced by specific genes, by hormones, by anatomy, or by social learning. Some of the differences are entirely physical (e.g., presence of a uterus) and some differences are just as obviously purely a matter of social learning and custom (e.g., relative hair length). Many differences, though, such as gender identity, appear to be influenced by both biological and social factors (“nature” and “nurture”).

The early stages of human differentiation appear to be quite similar to the same biological processes in other mammals and the interaction of genes, hormones and body structures is fairly well understood. In the first weeks of life, a fetus has no anatomic or hormonal sex, and only a karyotype distinguishes male from female. Specific genes induce gonadal differences, which produce hormonal differences, which cause anatomic differences, leading to psychological and behavioral differences, some of which are innate and some induced by the social environment.

Humans, many mammals, insects and other animals have an XY sex-determination system. Humans have forty-six chromosomes, including two sex chromosomes, XX in females and XY in males. It is obvious that the Y chromosome must carry at least one essential gene which determines testicular formation (originally termed TDF). A gene in the sex-determining region of the short arm of the Y, now referred to as SRY, has been found to direct production of a protein, testis determining factor, which binds to DNA, inducing differentiation of cells derived from the genital ridges into testes. In transgenic XX mice (and some human XX males), SRY alone is sufficient to induce male differentiation.

Various processes are involved in the development of sex differences in humans. Sexual differentiation in humans includes development of different genitalia and the internal genital tracts, breasts, body hair, and plays a role in gender identification.[1]

The development of sexual differences begins with the XY sex-determination system that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between male and female humans from an undifferentiated zygote.[2] Atypical sexual development, and ambiguous genitalia, can be a result of genetic and hormonal factors.[3]

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Sexual differentiation – Wikipedia, the free encyclopedia

Sex – Wikipedia, the free encyclopedia

Organisms of many species are specialized into male and female varieties, each known as a sex.[1]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). By definition, male gametes are small, motile, and optimized to transport their genetic information over a distance, while female gametes are large, non-motile and contain the nutrients necessary for the early development of the young organism. 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.

The gametes produced by an organism determine 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[clarification needed] the sexes experience.

Sexual reproduction first probably evolved about a billion years ago within ancestral single-celled eukaryotes.[2] 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, and that sex helps in the removal of disadvantageous traits.

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.[3][4][5]

While the evolution of sex dates to the prokaryote or early eukaryote stage,[citation needed] the origin of chromosomal sex determination may have been fairly early in eukaryotes.[citation needed] The ZW sex-determination system is shared by birds, some fish and some crustaceans. Most mammals, but also some insects (Drosophila) and plants (Ginkgo) use XY sex-determination.[citation needed]X0 sex-determination is found in certain insects.

No genes are shared between the avian ZW and mammal XY chromosomes,[6] 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.[7]

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.[8] 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.[9] 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).[10] 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.[11]

Most sexually reproducing animals spend their lives as diploid organisms, with the haploid stage reduced to single cell gametes.[12] The gametes of animals have male and female formsspermatozoa and egg cells. These gametes combine to form embryos which develop into a new organism.

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Sex – Wikipedia, the free encyclopedia

Pathology and Genetics of Tumours of the Breast and Female …

This WHO classification covers the female and male breast, ovaries, fallopian tumors, uterine cervix, uterine corpus, vulva, vagina and inherited tumor syndromes. It includes a comprehensive classification of benign and malignant neoplasms. Targeted readership includes pathologists, gynaecologists, surgeons, oncologists, and basic scientists. Similar to the previous volumes of the series, the book includes numerous color photographs, magnetic resonance images, CT scans and charts. In addition to its pathology and genetics, each lesion is described with its epidemiology, etiology, clinical features, as well as prognosis and predictive factors.

This book is in the series commonly referred to as the “Blue Book” series. Pathology and Genetics of Tumors of the Breast and Female Genital Organs

Contributors::Dr Vera M. Abeler, Dr Jorge Albores-Saavedra, Dr Isabel Alvarado-Cabrero, Dr Erik Sgaard Andersen, Dr Alan Ashworth, Dr Jean-Pierre Bellocq, Dr Christine Bergeron, Dr Ross S. Berkowitz, Dr Werner Bcker, Dr Anne-Lise Brresen-Dale, Dr Annegien Broeks, Dr C. Hilary Buckley, Dr Gianni Bussolati,Dr Rosmarie Caduff,Dr Maria-Luisa Carcangiu, Dr Silvestro Carinelli, Dr Annie N. Cheung, Dr Anne-Marie Cleton-Jansen, Dr Cees J. Cornelisse, Dr Christopher P. Crum, Dr Bruno Cutuli, Dr Peter Devilee, Dr Mojgan Devouassoux-Shisheboran, Dr Manfred Dietel, Dr Stephen Dobbs, Dr Maria Drijkoningen, Dr Douglas Easton, Dr Rosalind Eeles, Dr Ian O. Ellis, Dr Charis Eng, Dr Vincenzo Eusebi, Dr Mathias Fehr, Dr Rosemary A. Fisher, Dr Riccardo Fodde, Dr Silvia Franceschi, Dr Shingo Fujii, Dr David R. Genest, Dr Deborah J. Gersell, Dr Blake Gilks, Dr David E. Goldgar,Dr Annekathryn Goodman,Dr Pierre Hainaut, Dr Janet Hall, Dr Urs Haller, Dr Antonius G.J.M. Hanselaar, Dr Steffen Hauptmann, Dr Michael R. Hendrickson, Dr Sylvia H. Heywang-Kbrunner, Dr Heinz Hfler, Dr Roland Holland, Dr Jocelyne Jacquemier, Dr Rudolf Kaaks, Dr Apollon I. Karseladze, Dr Richard L. Kempson, Dr Takako Kiyokawa, Dr Ikuo Konishi, Dr Rahel Kubik-Huch, Dr Robert J. Kurman, Dr Sunil R. Lakhani, Dr Janez Lamovec, Dr Salvatore Lanzafame, Dr Sigurd Lax, Dr Kenneth R. Lee, Dr Fabio Levi, Dr Gatan Macgrogan, Dr Gaetano Magro, Dr Kien T. Mai, Dr W. Glenn Mccluggage, Dr Hanne Meijers-Heijboer, Dr Rosemary R. Millis, Dr Farid Moinfar, Dr Samuel C. Mok, Dr Alvaro N. Monteiro, Dr Eoghan E. Mooney, Dr Philippe Morice, Dr Hans Morreau, Dr Kiyoshi Mukai, Dr Mary Murnaghan, Dr George L. Mutter, Dr Steven Narod, Dr Jahn M. Nesland, Dr Edward S. Newlands, Dr Bernt B. Nielsen, Dr Francisco F. Nogales, Dr Hiroko Ohgaki, Dr Magali Olivier, Dr Andrew G. str, Dr Jorma Paavonen, Dr Paivi Peltomak, Dr Johannes L. Peterse, Dr Jurgen J.M. Piek, Dr Paola Pisani, Dr Steven Piver, Dr Jaime Prat, Dr Klaus Prechtel, Dr Dieter Prechtel, Dr Usha Raju, Dr Juan Rosai, Dr Lawrence M. Roth, Dr Peter Russell, Dr Joanne K.L. Rutgers, Dr Rengaswamy Sankaranarayanan, Dr Anna Sapino, Dr Annie J. Sasco, Dr Xavier Sastre-Garau, Dr Stuart J. Schnitt, Dr John O. Schorge, Dr Peter E. Schwartz, Dr Robert E. Scully, Dr Hideto Senzaki, Dr Elvio G. Silva, Dr Steven G. Silverberg, Dr Jorge Soares, Dr Leslie H. Sobin, Ms Nayanta Sodha Msc, Dr Mike R. Stratton, Dr Csilla Szabo, Dr Lszl Tabr, Dr Aleksander Talerman, Dr Colette Taranger-Charpin, Dr Fattaneh A. Tavassoli, Dr. Antonio Bernardino Almeida, Dr Massimo Tommasino, Dr Airo Tsubura, Dr Paul J. Van Diest, Dr Laura J. Vant Veer, Dr Russell S. Vang, Dr Hans F.A. Vasen, Dr A.R. Venkitaraman, Dr Ren H.M. Verheijen, Dr William R. Welch, Dr Michael Wells, Dr Edward J. Wilkinson, Dr Andrew Wotherspoon,

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Pathology and Genetics of Tumours of the Breast and Female …

Female Age and Chromosome Problems in Eggs and Embryos

Structural abnormalities where there is a problem with the structure of a chromosome Examples include translocations, duplications and deletions of part of a chromosome

Aneuploid eggs and embryos are also responsible for most of the decline in overall fertility with female aging – and for the low pregnancy success rates with IVF for women over 40.

The increased rate of chromosomal abnormalities in women of advanced reproductive age has been well documented in research studies. The graph below shows the rate of chromosomally abnormal IVF eggs by female age. These numbers are approximate and compiled from several studies.

We do not know exactly why there is an increase in chromosomal abnormalities in the eggs of women as they age. However, research studies have clarified some of the issues involved.

The meiotic spindle is a critical component of eggs that is involved in organizing the chromosome pairs so that a proper division of the pairs can occur as the egg is developing. An abnormal spindle can predispose to development of chromosomally abnormal eggs.

An excellent study published in the medical journal “Human Reproduction” in October of 1996 investigated the influence of maternal age on meiotic spindle assembly in human eggs.

The pictures below are from this journal article. These photos were taken with confocal fluorescence microscopy of eggs stained with special dyes to show the spindles and chromosomes.

When the chromosomes line up properly in a straight line on the spindle apparatus in the egg, the division process would be expected to proceed normally so that the egg would end up with its proper complement of 23 chromosomes.

However, with a disordered arrangement on an abnormal spindle, the division process may be uneven – resulting in an unbalanced chromosomal situation in the egg.

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Female Age and Chromosome Problems in Eggs and Embryos

Difference between Male and Female Chromosomes

Curious to know what determines the gender of a baby?

The mystery lies in the chromosomes. The knowledge of chromosomes is essential for understanding human genetics. The field has attracted much research and everyday there are ongoing discoveries. Human cells consist of 46 chromosomes which make 23 pairs. In males and females, the first 22 are similar across both genders and are known as autosomes. The last one pair (23rd) is known as the sex chromosome and makes all the difference.

The sex chromosome of females contains two Xs while that for males contains one Y and one X. The presence of this last chromosome pair determines the gender of a baby. Apart from the X and Y difference, these chromosomes have many other differences which form the characteristics of the two genders. Knowing these differences is going to help you understand the differences between the genetic make up of the two genders and pave way for more research.

The behaviour of this X chromosome in males is different from those in the female chromosome.

The female chromosome has more working genes than the male one. It is known to have more than 1000 working genes while the male chromosome has less than 100. Of these 1000 working genes, 200 to 300 are gender specific while the remaining are shared across the two genders.

Average female chromosomes are recorded to be greater in size than male chromosome. Exceptions may occur but these are the average measurements. The specific cause for this is not known yet.

1

Female Chromosome:

The female sex chromosome pair does not contain any Y chromosome. The pair is an XX and the two X chromosomes are equal in size and chromosomal pairing.

An additional X chromosome, giving an XXX configuration, results in triple X syndrome where a women is taller than others and has an average IQ. If there is just one X in the sex chromosome, the Turners syndrome occurs where a born female is shorter, infertile and lower in IQ level than those with normal XX pairs.

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Difference between Male and Female Chromosomes

Galaxy Of Genetic Differences Between Men & Women

Scientists have found genetic evidence for what some men have long suspected: it is dangerous to make assumptions about women. The key is the X chromosome, the “female” sex chromosome that all men and women have in common. In a study published this week in the journal Nature, scientists said they had found an unexpectedly large genetic variation in the way parts of womens two X chromosomes are distributed among them. The findings were published in conjunction with the first comprehensive decoding of the chromosome. Females can differ from each other almost as much as they do from males in the way many genes at the heart of sexual identity behave, researchers say. “Literally every one of the females we looked at had a different genetic story,” says Duke University genetics expert Huntington Willard, who co-wrote the study. “It is not just a little bit of variation.” The analysis also found that the obsessively debated differences between men and women were, at least on the genetic level, even greater than previously thought. As many as 300 of the genes on the X chromosomes may be activated differently in women than in men, says the other author of the paper, Laura Carrel, molecular biologist at the Pennsylvania State University College of Medicine. The newly discovered genetic variation between women might help account for differing gender reactions to prescription drugs and the heightened vulnerability of women to some diseases, experts say. “The important question becomes how men and women actually vary and how much variability there is in females,” Carrel says. “We now might have new candidate genes that could explain differences between men and women.” All told, men and women may differ by as much as 2 per cent of their entire genetic inheritance, greater than the hereditary gap between humankind and its closest relative, the chimpanzee. “In essence,” Willard says, “there is not one human genome, but two: male and female.” SCIENTISTS estimate that there may be as many as 30,000 genes in the chemical DNA blueprint for human growth and development known as the human genome. The genes are parcelled in 23 pairs of rod-like structures called chromosomes, which are contained in every cell of the body. The most distinctive of the chromosomes are the mismatched pair of X and Y chromosomes that guide sexual development. Until now, researchers considered the shuffle of sex chromosomes at conception a simple matter of genetic roulette. The chromosomes that dictate sexual development are mixed and matched in predictable combinations: A female inherits one X chromosome from each parent; a male inherits an X chromosome from his mother and a Y chromosome from his father. To avoid any toxic effect from double sets of X genes, female cells randomly choose one copy of the X chromosome and “silence” it – or so scientists had believed. The new analysis found that the second X chromosome was not a silent partner. As many as 25 per cent of its genes are active, serving as blueprints to make necessary proteins. To investigate this variation, Carrel and Willard isolated cells from 40 women and measured the activity of hundreds of genes to see whether those on the second X chromosome were active or silent. Although those extra genes were supposed to be turned off, they found that about 15 per cent of them in all female cells were still active, or “expressed”. In some women, up to an additional 10 per cent of those X-linked genes showed varying patterns of activity. “This is 200 to 300 genes that are expressed up to twice as much as in a male or some other females,” Willard says. “This is a huge number.” Researchers were surprised that they found so many unexpected differences in the behaviour of the one sex chromosome that men and women share. Though there is dramatic variation in the activation of genes on the X chromosomes that women inherit, there is none among those in men, the researchers reported. Researchers have yet to understand the effect of so many different patterns of gene activation among women, or determine what controls them, but all the evidence suggests that they are not random. ILLUMINATING this complex palette was the work of an international team of 250 scientists, led by geneticist Mark Ross, at the Wellcome Trust Sanger Institute in Hinxton, Cambridge. The team produced the first complete sequence of the X chromosome about two years after the decoding of the male Y chromosome. The researchers found that the X chromosome, though relatively poor in genes, is rich in influence, deceptively subtle, and occasionally deadly to males. The international team identified 1,098 functional genes along the X chromosome, more than 14 times as many as scientists had located on the tiny Y chromosome. Even so, the researchers say, there are fewer genes to be found on the X chromosome than on any of the other 22 chromosomes sequenced so far. Most of the X genes are slightly smaller than average. But one is the largest known gene in the human genome, a segment of DNA linked to diseases such as muscular dystrophy, that is more than 2.2 million characters long. The X chromosome contains a larger share of genes linked to disease than any other chromosome. It is implicated in 300 hereditary disorders, including colour blindness, haemophilia and Duchenne muscular dystrophy. Nearly 10 per cent of the genes may belong to a group known to be more active in testicular cancers, melanomas and other cancers, the team reports. “The biggest surprise for us was just how many of these [cancer-related] genes there are on the X,” Ross says. The complete gene sequence provided some clues to the origins of the human sex chromosomes. The researchers found that most of the genes on the X chromosome also reside on chromosome 1 and chromosome 4 of chickens. That supports the theory that the human sex chromosomes evolved from a regular pair of chromosomes from a common ancestor of chickens and humans – about 300 million years ago. 2005 Scotsman.com http://news.scotsman.com/scitech.cfm?id=295472005

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Galaxy Of Genetic Differences Between Men & Women

How Chromosomes Determine Sex – About

Karyotype of a normal male with 22 pairs of autosomes and one pair of sex chromosomes. U.S. Department of Energy Human Genome Program

How Chromosomes Determine Sex:

Chromosomes are long, stringy aggregates of genes that carry heredity information. They are composed of DNA and proteins and are located within the nucleus of our cells. Chromosomes determine everything from hair color and eye color to sex. Whether you are a male or female depends on the presence or absence of certain chromosomes.

Human cells contain 23 pairs of chromosomes for a total of 46.

There are 22 pairs of autosomes and one pair of sex chromosomes. The sex chromosomes are the X chromosome and the Y chromosome.

Sex Chromosomes:

In human sexual reproduction, two distinct gametes fuse to form a zygote. Gametes are reproductive cells produced by a type of cell division called meiosis. Gametes are also called sex cells. They contain only one set of chromosomes and are said to be haploid.

The male gamete, called the spermatozoan, is relatively motile and usually has a flagellum. The female gamete, called the ovum, is nonmotile and relatively large in comparison to the male gamete. When the haploid male and female gametes unite in a process called fertilization, they form what is called a zygote. The zygote is diploid, meaning that it contains two sets of chromosomes.

Sex Chromosomes X-Y:

The male gametes or sperm cells in humans and other mammals are heterogametic and contain one of two types of sex chromosomes. They are either X or Y. The female gametes or eggs however, contain only the X sex chromosome and are homogametic.

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How Chromosomes Determine Sex – About

X chromosome – Genetics Home Reference

Reviewed January 2012

The X chromosome is one of the two sex chromosomes in humans (the other is the Y chromosome). The sex chromosomes form one of the 23 pairs of human chromosomes in each cell. The X chromosome spans about 155 million DNA building blocks (base pairs) and represents approximately 5 percent of the total DNA in cells.

Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, while males have one X and one Y chromosome. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in cells other than egg cells. This phenomenon is called X-inactivation or Lyonization. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.

Some genes on the X chromosome escape X-inactivation. Many of these genes are located at the ends of each arm of the X chromosome in areas known as the pseudoautosomal regions. Although many genes are unique to the X chromosome, genes in the pseudoautosomal regions are present on both sex chromosomes. As a result, men and women each have two functional copies of these genes. Many genes in the pseudoautosomal regions are essential for normal development.

Identifying genes on each chromosome is an active area of genetic research. Because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. The X chromosome likely contains 800 to 900 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

Genes on the X chromosome are among the estimated 20,000 to 25,000 total genes in the human genome.

Many genetic conditions are related to changes in particular genes on the X chromosome. This list of disorders associated with genes on the X chromosome provides links to additional information.

Changes in the structure or number of copies of a chromosome can also cause problems with health and development. The following chromosomal conditions are associated with such changes in the X chromosome.

In most individuals with 46,XX testicular disorder of sex development, the condition results from an abnormal exchange of genetic material between chromosomes (translocation). This exchange occurs as a random event during the formation of sperm cells in the affected person’s father. The translocation affects the gene responsible for development of a fetus into a male (the SRY gene). The SRY gene, which is normally found on the Y chromosome, is misplaced in this disorder, almost always onto an X chromosome. A fetus with an X chromosome that carries the SRY gene will develop as a male despite not having a Y chromosome.

48,XXYY syndrome is caused by the presence of an extra X chromosome and an extra Y chromosome in a male’s cells. Extra genetic material from the X chromosome interferes with male sexual development, preventing the testes from functioning normally and reducing the levels of testosterone in adolescent and adult males. Extra copies of genes from the pseudoautosomal regions of the extra X and Y chromosome contribute to the signs and symptoms of 48,XXYY syndrome; however, the specific genes have not been identified.

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X chromosome – Genetics Home Reference

Impact of Genetic Selection on Female Fertility – eXtension

Prospects for improving female fertility in dairy cattle via genetic selection are reviewed. Today’s high-producing cows have shorter estrous cycles, fewer standing events, shorter duration of estrus, and more frequent multiple ovulations. Although high milk production is often implicated as the cause of impaired fertility, the impact of inadequate body condition appears to be greater, as the latter has a significant impact on probability of conception, rate of embryonic loss, and proportion of anestrous animals. Genetic improvement of female fertility can be achieved by indirect selection for productive life (PL) or body condition score (BCS), or by direct selection for traits such as daughter pregnancy rate (DPR). Most leading dairy countries have implemented genetic evaluation systems for female fertility in the past decade, but refinement of these systems to account for hormonal synchronization, differences in the voluntary waiting period, exposure to natural service bulls, and other confounding factors is warranted. Recent work has focused on the development of data collection and genetic evaluation systems that will allow selection of bulls that have daughters that are resistant to common health disorders, including mastitis, lameness, ketosis, displaced abomasum, and metritis. Such systems will allow selection of animals that can remain healthy and fertile while producing large quantities of milk.

The challenges associated with achieving pregnancy in modern, high-producing dairy cows have received considerable attention from scientists, veterinarians, and farmers in recent years. Todays dairy cows tend to have lower conception rate, greater days open, and greater likelihood of culling due to infertility than their counterparts from two or three decades ago. Genetic selection programs have led to rapid gains in milk yield and conformation traits; but performance for traits such as female fertility, longevity, and susceptibility to disease has tended to decline. While it is impossible to completely disentangle the effects of selection from simultaneous changes in nutrition, cow care, and reproductive management, it is clear that geneticists failed to pay adequate attention to health, fertility, and longevity traits until the past decade. The magnitude of genetic variation in such traits is surprising, and we are now poised to take advantage of recent research and development efforts regarding the definition, measurement, and genetic analysis of these traits.

The objective of this paper is to review the relationships between female fertility and other economically important dairy traits and to discuss opportunities for improving reproductive performance through direct selection of highly fertile animals or indirect selection of animals that maintain adequate body condition and resist metabolic and infectious diseases during lactation.

Please check this link first if you are interested in organic or specialty dairy production

Milk production of dairy cows on modern commercial farms has roughly doubled over the past four decades. First parity cows on large commercial dairy farms typically peak at 40 to 45 kg/d, while second and later parity cows typically peak at 50 to 55 kg/d. Furthermore, each group typically sustains daily milk production of 40 kg/d or more during the first seven months postpartum. Therefore, one might expect differences in the reproduction of high-producing cows, as compared with low-producing cows or yearling heifers.

Lopez et al. (2005) discussed some of the differences between the reproductive biology of lactating Holstein cows and yearling Holstein heifers. In particular, Lopez et al. (2005) noted that lactating cows have shorter duration of estrus (7 to 8 hr vs. 11 to 14 hr), longer and more variable estrous cycles (20 to 29 d vs. 20 to 23 d), larger diameter of ovulatory follicles (16 to18 mm vs. 14 to 16 mm), and greater rates of anovulation (20 to 30% vs. 1 to 2%), multiple ovulation (20 to 25% vs. 1 to 3%), and pregnancy loss (20 to 30% vs. 3 to 5%).

Lopez et al. (2005) also documented differences in these characteristics between lactating cows according to levels of milk production. They (Lopez et al., 2005) used the HeatWatch system (DDx Inc., Denver, Colorado) to monitor the estrous characteristics of 146 high-producing Holstein cows (46.4 kg/d for the 10 d preceding estrus) and 177 low-producing Holstein cows (33.5 kg/d for the 10 d preceding estrus). High-producing cows had shorter duration of estrus (6.2 hr vs. 10.9 hr), fewer standing events (6.3 vs. 8.8), and shorter standing time per event (21.7 sec vs. 28.2 sec). Duration of estrus decreased linearly from 14.7 hr for cows milking 25 to 30 kg/d to 2.8 hr for cows milking 50 to 55 kg/d. In addition, the percentage of cows with multiple ovulations increased from 0.0% for cows milking between 25 and 30 kg/d to 51.6% for cows between 50 and 55 kg/d.

The rate of early embryonic loss in Holstein cows is also a major concern, as noted in several recent studies that have used ultrasound for pregnancy detection at 27 to 31 d after breeding, followed by pregnancy confirmation via rectal palpation at 39 to 48 d after breeding. Reported rates of embryonic loss during this interval ranged from 0.70 to 1.40% per day (e.g., Cartmill et al., 2001; Cerri et al., 2004; Santos et al., 2004). However, estimates of the rate of embryonic loss (particularly those from commercial farms) may be biased upward by false positive diagnoses at the early ultrasound exam, as most veterinarians tend to use caution when declaring cows as non-pregnant in herds that use hormonal resynchronization programs.

On large western dairy farms, mean veterinary-confirmed conception rates of Holstein cows at 75 d after breeding were nearly constant over the first five inseminations (0.30, 0.31, 0.31, 0.29, and 0.28, respectively), while means for Jersey cows declined linearly from the first through fifth insemination (0.42, 0.38, 0.34, 0.29, and 0.27, respectively). Mean conception rate at first service tended to decline with age in both breeds (0.35, 0.29, 0.28, 0.26, and 0.25, respectively, for first through fifth parity Holsteins and 0.44, 0.43, 0.41, 0.39, and 0.37, respectively, for first through fifth parity Jerseys), though the rate of decline was less noticeable for repeat inseminations than for first insemination (Weigel, 2006 (unpublished)). Both breeds have been selected for many generations under similar management conditions, and both have made rapid genetic progress over the past three decades (mean mature equivalent 305 d milk yield increased from 6,904 to 11,608 kg in Holsteins and from 4,461 kg to 8,273 kg in Jerseys from 1970 to 2000). Differences in mean conception rate within the Holstein breed were found among cows at different levels of daily milk yield, but such differences were smaller than one might expect (Weigel, 2005 (unpublished)). Mean conception rates at 75 d after breeding were 0.33, 0.33, and 0.32 for primiparous Holstein cows that averaged 36 kg/d, respectively, during the first 3 mo of lactation; whereas corresponding means were 0.28, 0.28, and 0.27 for multiparous Holstein cows that averaged 45 kg/d, respectively. In Wisconsin Holsteins, Lopez et al. (2005) found no relationship between the percentage of cows exhibiting anovulatory condition and level of daily milk yield. The percentage of anovular cows was 27.8% for cows that were milking 25 to 30 kg/d and 26.3% for cows that were milking 50 to 55 kg/d (means for 5-kg intervals in between ranged from 21.7% to 35.1%, with no apparent trend). In California Holsteins, Santos et al. (2004) found a weak, nonsignificant relationship between milk yield and rate of embryonic loss between 31 and 45 d after breeding, with rates of 9.7% for cows that were milking 36 kg/d and 12.7% for cows that were milking 52 kg/d. Thus, it does not appear that increased milk yield is solely responsible for the decline in mean reproductive performance.

High milk production, whether achieved through genetic selection, enhanced nutrition, or improved management, is often implicated as the cause of health, fertility, and culling problems on modern dairy farms. However, a complex relationship exists between milk yield, health, and reproductive performance. High-producing cows tend to be more susceptible to metabolic disorders and infectious diseases, and these can lead to impaired fertility. On the other hand, healthy cows tend to have higher milk production and greater reproductive performance than unhealthy cows. Conversely, cows that remain nonpregnant for much of the lactation tend to achieve higher levels of total production because fewer resources are allocated to the developing calf. Thus, one must be cautious when attempting to formulate cause-effect relationships between these traits.

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Impact of Genetic Selection on Female Fertility – eXtension

Female – Wikipedia, the free encyclopedia

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

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

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

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

The word female comes from the Latin femella, the diminutive form of femina, meaning “woman”. It is not etymologically related to the word male, but in the late 14th century the spelling was altered in English to parallel the spelling of male.[2]

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

Most mammalian females have two copies of the X chromosome as opposed to the male which carries only one X and one smaller Y chromosome (but some mammals, such as the Platypus, have different combinations). To compensate for the difference in size, one of the female’s X chromosomes is randomly inactivated in each cell of placental mammals while the paternally derived X is inactived in marsupials. In birds and some reptiles, by contrast, it is the female which is heterozygous and carries a Z and a W chromosome whilst the male carries two Z chromosomes. Intersex conditions can also give rise to other combinations, but this usually results in sterility.

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

A common symbol used to represent the female sex is (Unicode: U+2640 Alt codes: Alt+12), a circle with a small cross underneath. According to Schott,[3] the most established view is that the male and female symbols “are derived from contractions in Greek script of the Greek names of these planets, namely Thouros (Mars) and Phosphoros (Venus). These derivations have been traced by Renkama[4] who illustrated how Greek letters can be transformed into the graphic male and female symbols still recognised today.” Thouros was abbreviated by , and Phosphoros by , which were contracted into the modern symbols.

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

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Definition Of female reproductive system |Genetic …

The human female reproductive system (or female genital system) contains two main parts: the uterus, which hosts the developing fetus, produces vaginal and uterine secretions, and passes the male’s sperm through to the fallopian tubes; and the ovaries, which produce the female’s egg cells. These parts are internal; the vagina meets the external organs at the vulva, which includes the labia, clitoris and urethra. The vagina is attached to the uterus through the cervix, while the uterus is attached to the ovaries via the Fallopian tubes. At certain intervals, the ovaries release an ovum, which passes through the Fallopian tube into the uterus. If, in this transit, it meets with sperm, the sperm penetrate and merge with the egg, fertilizing it.

During the reproductive process, the egg releases certain molecules that are essential to guiding the sperm and these allow the surface of the egg to attach to the sperm’s surface then the egg can absorb the sperm and fertilization begins. The fertilization usually occurs in the oviducts, but can happen in the uterus itself. The zygote then implants itself in the wall of the uterus, where it begins the processes of embryogenesis and morphogenesis. When developed enough to survive outside the womb, the cervix dilates and contractions of the uterus propel the fetus through the birth canal, which is the vagina.

The ova are larger than sperm and have formed by the time a female is born. Approximately every month, a process of oogenesis matures one ovum to be sent down the Fallopian tube attached to its ovary in anticipation of fertilization. If not fertilized, this egg is flushed out of the system through menstruation.

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Definition Of female reproductive system |Genetic …

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