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A gay Gene – Is Homosexuality Inherited Assault On Gay …

Historians of homosexuality will judge much twentieth-century “science” harshly when they come to reflect on the prejudice, myth, and downright dishonesty that litter modern academic research on sexuality. Take, for example, the lugubrious statements of-once respected investigators. Here is Sandor Feldman, a well-known psychotherapist, in 1956:

Or consider the remarks of the respected criminologist Herbert Hendin:

The notion of the homosexual as a deeply disturbed deviant in need of treatment was the orthodoxy until only recently. Bernard Oliver, Jr., a psychiatrist specializing in sexual medicine, wrote in 1967 that Dr. Edmond Bergler feels that the homosexual’s real enemy is not so much his perversion but [sic] ignorance of the possibility that he can be helped, plus his psychic masochism which leads him to shun treatment….

There is good reason to believe now, more than ever before, that many homosexuals can be successfully treated by psychotherapy, and we should encourage homosexuals to seek this help.[3]

Such views about the origin of homosexual preferences have become part of American political culture as well. When, in 1992, Vice-President Dan Quayle offered the view that homosexuality “is more of a choice than a biological situation…. It is a wrong choice,”[4] he merely reasserted the belief that homosexuality reflected psychological conditioning with little biological basis, and certainly without being influenced by a person’s biological inheritance.

And now we have the much publicized spectacle–Time magazine has taken up the story in a dramatic feature entitled “Search for a Gay Gene”[5] –of homosexuality’s origins being revealed in the lowly fruit fly, Drosophila.[6] Males and females of this, one has to admit, rather distant relation adopt courtship behavior that has led two researchers at the US National Institutes of Health to draw extravagant parallels with human beings.

Shang-Ding Zhang and Ward F. Odenwald found that what they took to be homosexual behavior among male fruit flies–touching male partners with forelegs, licking their genitalia, and curling their bodies to allow genital contact–could be induced by techniques that abnormally activated a gene called w (for “white,” so called because of its effect on eye color). Widespread activation (or “expression”) of the white gene in Drosophila produced male-to-male rituals that took place in chains or circles of five or more flies. If female fruit flies lurked nearby, male flies would only rarely be tempted away from their male companions. These findings, which have apparently been reproduced by others, have led the investigators to conclude that “w misexpression has a profound effect on male sexual behavior.”

Zhang and Odenwald go on to speculate that the expression of w could lead to severe shortages of serotonin, an important chemical signal that enables nerve cells to communicate with one another. The authors conjecture that mass activation of w diminishes brain serotonin by promoting its use elsewhere in the body. Indeed, cats, rabbits, and rats all show some elements of “gay” behavior when their brain serotonin concentrations fall. Intriguing and, you might think, convincing evidence.

Yet, although w is found in modified form in human beings, it is a huge (and, it seems to me, a dangerous) leap to extrapolate observations from fruit flies to humans. In truth, when the recent data are interpreted literally we find that (a) the w gene induces male group sex behavior in highly ritualized linear or circular configurations, and (b) while these tend more toward homosexual than straight preferences, they are truly bisexual (as pointed out by Larry Thompson in Time). Zhang and Odenwald force their experimental results with fruit flies to fit their preconceived notions of homosexuality. How simplistic it seems to equate genital licking in Drosophila with complex individual and social homosexual behavior patterns in humans. Can notions of homosexuality apply uniformly across the biological gulf that divides human beings and insects? Such arguments by analogy seem hopelessly inadequate.

By contrast, the work of Simon LeVay, Dean Hamer, and a small group of researchers concerned to distinguish biological and genetic influences on sexual behavior has discredited much of the loose rhetoric that has been used about homosexuality. In August 1991, LeVay, a neuroscientist who now directs the Institute of Gay and Lesbian Education in southern California, published in the magazine Science findings from autopsies of men and women of known sexual preference. He found that a tiny region in the center of the brain–the interstitial nucleus of the anterior hypothalamus (INAH) 3–was, on average, substantially smaller in nineteen gay men who died from AIDS than among sixteen heterosexual men.[7]

The observation that the male brain could take two different forms, depending on one’s sexual preference, was a stunning discovery. The hypothalamus-a small, intricate mass of cells lying at the base of the brain-was long believed to have a role in sexual behavior, but direct evidence that it did so was weak. Yet LeVay expressed caution. Although his data showed that human sexual preference “is amenable to study at the biological level,” he noted that it was impossible to be certain whether the anatomical differences between the brains of gay and straight men were a cause or a consequence of their preference.[8]

In the thirteen persuasive essays that make up The Sexual Brain, LeVay takes account of the current bio-behavioral controversy over the science of sex. From the union of wiry sperm and bloated ovum to the child-rearing practices of mammals and humans, for which mothers are largely responsible, he writes (metaphorically), the “male is little more than a parasite who takes advantage of [the female’s] dedication to reproduction.” He goes on to draw from a wide range of sources to support his contentious assertion that “there are separate centers within the hypothalamus for the generation of male-typical and female-typical sexual behavior and feelings.” He argues that a connection–the details of which remain mysterious–between brain and behavior exists through hormones such as testosterone.

The most convincing evidence he puts forward to support his view comes from women with congenital adrenal hyperplasia. This condition, in which masculine characteristics, such as androgenized genitalia, including clitoral enlargement and partially fused labia, become pronounced in women, is caused by excessive testosterone production and leads, in adulthood, to an increased frequency of lesbianism affecting up to half of all the women who have the condition. The theory, still unproven, that is proposed to explain these behavioral effects of hormones is that one or more chemical signals act during a brief early critical period in the development of most males to alter permanently both the brain and the pattern of their later adult behavior. Unless this hormonal influence is switched on, a female pattern of development will follow automatically.

What might be the origin of biological differences underlying male sexual preference? In 1993 Dean Hamer and his colleagues at the National Cancer Institute discovered a preliminary but nevertheless tantalizing clue.[9] Hamer began his painstaking search for a genetic contribution to sexual behavior by studying the rates of homosexuality among male relatives of seventy-six known gay men. He found that the incidence of homosexual preference in these family members was strikingly higher (13.5 percent) than the rate of homosexuality among the whole sample (2 percent). When he looked at the patterns of sexual orientation among these families, he discovered more gay relatives on the maternal side. Homosexuality seemed, at least, to be passed from generation to generation through women.

Maternal inheritance could be explained if there was a gene influencing sexual orientation on the X chromosome, one of the two human sex chromosomes that bear genes determining the sex of offspring.[10] Men have both X and Y chromosomes, while women have two X chromosomes. A male sex-determining gene, called SRY, is found on the Y chromosome. Indeed, the Y chromosome is the most obvious site for defining male sexuality since it is the only one of the forty-six human chromosomes to be found in men alone. The SRY gene is the most likely candidate both to turn on a gene that prevents female development and to trigger testosterone production. Since the female has no Y chromosome, she lacks this masculinizing gene. In forty pairs of homosexual brothers, Hamer and his team looked for associations between the DNA on the X chromosome and the homosexual trait. They found that thirty-three pairs of brothers shared the same five X chromosomal DNA “markers,” or genetic signatures, at a region near the end of the long arm of the X chromosome designated Xq28.[11] The possibility that this observation could have occurred by chance was only 1 in 10,000.

LeVay takes a broad philosophical perspective in his discussion of human sexuality by placing his research in the context of animal evolution. Hamer, on the other hand, has written, with the assistance of the journalist Peter Copeland, a more focused popular account of his research. He conceived his project after reflecting on a decade of laborious research on yeast genes. Although the project was approved by the National Institutes of Health after navigating a labyrinthine course through government agencies, it remained rather meagerly funded.

Taken together, the scientific papers of both LeVay and Hamer and the books that their first reports have now spawned[12] make a forceful but by no means definitive case for the view that biological and genetic influences have an important–perhaps even decisive–part in determining sexual preference among males. LeVay writes, for example, that “…the scientific evidence presently available points to a strong influence of nature, and only a modest influence of nurture.” But there is no broad scientific agreement on these findings. They have become mired in a quasi-scientific debate that threatens to let obscurantism triumph over inquiry. What happened?

To begin with, we must ask what LeVay and Hamer have not shown. LeVay has found no proof of any direct link between the size of INAH 3 and sexual behavior. Size differences alone prove nothing. He was also unable to exclude the possibility that AIDS has an influence on brain structure, although this seemed unlikely, since six of the heterosexual men he studied also had AIDS. Moreover, Hamer did not find a gene for homosexuality; what he discovered was data suggesting some influence of one or more genes on one particular type of sexual preference in one group of people. Seven pairs of brothers did not have the Xq28 genetic marker, yet these brothers were all gay. Xq28 is clearly not a sine qua non for homosexuality; it is neither a necessary nor a sufficient cause by itself.

And what about women? Although the genitalia of women as well as men are clearly biologically determined, no data exist to prove a genetic link, or a link based on brain structure, with female sexual preferences, whether heterosexual or homosexual. Finally, neither study has been replicated by other researchers, the necessary standard of scientific proof. Indeed, there is every reason to suppose that the INAH 3 data will be extremely difficult to confirm. Only a few years ago INAH 1 (located close to INAH 3) was also thought to be larger in men than in women. Two groups, including LeVay’s, have failed to reproduce this result.

Most of these limitations are clearly acknowledged by both LeVay and Hamer in their original scientific papers and are reinforced at length in their books. But reactions to their findings have nevertheless been harshly critical. For instance, after pointing out several potential weaknesses in Hamer’s study and criticizing his decision to publish in Science at a time when gay “lives are at stake,” two biologists, Anne Fausto-Sterling and Evan Balaban, asked “whether it might not have been prudent for the authors and the editors of Science to have waited until more of the holes in the study had been plugged….”[13] Fortunately, their somewhat hysterical reaction has been followed by more careful comment by other scientists.[14]

Lack of prudence also characterized the response in the press. In London, the conservative Daily Telegraph ran the clumsy headline, “Claim that homosexuality is inherited prompts fears that science could be used to eradicate it.” Another story began, “A lot of mothers are going to feel guilty,” while another was entitled “Genetic tyranny.”

These headlines are part of the popular rhetoric about DNA, which supposes that a gene represents an irreducible and immutable unit of the human self. The correlation between a potentially active gene and a behavior pattern is assumed to indicate cause and effect. Was Hamer himself guilty of over-interpretation? In his original paper, he went to extraordinary lengths to qualify his findings. He and his co-authors offer no fewer than ten statements advising a cautious reading of their data, and they note that “replication and confirmation of our results are essential.” Neither the hyperbolic press response with its relentless message of genetic determinism nor the ill-judged scientific criticism was appropriate.

Nevertheless, there are three conceptual issues raised by these reports –namely, heritability, sexual categorization, and the meaning of the phrase “biological basis of behavior” –which have been largely ignored in the scramble to publish instant analyses of the findings of LeVay and Hamer, among others.

Heritability is a measure of the resemblance between relatives; it is expressed as the proportion of variability in an observable characteristic that can be attributed to genetic factors. Eye color, for example, is 100 percent heritable, whereas we know that most behavioral traits have genetic contributions of well below 50 percent. Heritability is a quarrelsome issue among geneticists, and its proportional value is often quoted without the necessary qualifications. Variation in any trait is accounted for by the influence of genes (including, importantly, the interaction among genes), environment (the family and one’s wider life experience), and the interaction between one or more genes and one or more environmental variables. The standard measure of heritability is the sum of all genetic influences, and it ignores potentially complex interactions–for example, the influence of the family milieu on the behavioral expression of a gene influencing sexual preference. The most common error made by those who discuss genetic contributions to behavior is to forget that heritability is a property only of the population under study at one particular time. It cannot be generalized to characterize the behavior itself.

When we apply these considerations to Hamer’s data, we make a surprising discovery. If we accept his own hypothesis of the relation between the Xq28 marker and the behavioral trait, the maximum heritability of homosexuality in the group he studied is 67 percent, which may seem a remarkably high figure. Yet this group was a particularly selected one: the seventy-six study participants openly acknowledged being gay, and had volunteered for the study. What Hamer’s results do not tell us is what the influence of the Xq28 marker in the general population might be. He infers from various mathematical calculations “that Xq28 plays some role in about 5 to 30 percent of gay men.” But he admits that this is merely a preliminary estimate and that accurate measuring of Xq28 heritability in the general population remains to be done. In fact, a frequent criticism of Hamer’s Science paper was that he did not measure the incidence of Xq28 markers among heterosexual brothers of gay sibling pairs. Without this information, it is impossible to guess the influence of any genes that might be located at Xq28. Their effects will be unpredictable at best, and any interaction with the environment will assume critical importance.

At this point, science inches uneasily toward dogma and diatribe. Hamer cites Richard Lewontin’s Not in Our Genes[15] as one of his early inspirations to change the direction of his research. Hamer writes that he

knew that [Lewontin] had criticized the idea that behavior is genetic, arguing instead that it is a product of class-based social structures….Why was Lewontin, a formidable geneticist, so determined not to believe that behavior could be inherited? He couldn’t disprove the genetics of behavior in a lab, so he wrote a political polemic against it.

Indeed, Lewontin has frequently provided cogent arguments against the view that heritability can help delineate the effects of genes on human behavior.[16] He has described the separation of behavioral variation into genetic and environmental contributions and the interaction between the two as “illusory.”[17] For him and his co-writers, such a model “cannot produce information about causes of phenotypic difference,” i.e., differences in observable physical and mental traits. The precise meaning of heritability forces the inevitable conclusion, Lewontin has written, that whatever proportion is quoted, it “is nearly equivalent to no information at all for any serious problem in human genetics.”

Imagine Dean Hamer’s astonishment, therefore, when he received a letter from Richard Lewontin in 1992. A Harvard professor teaching genetics and behavior had invited Hamer to submit a pamphlet describing his research as an example of “conceptual advances” in “modern behavior genetic studies.” He had willingly complied, but only later discovered that it had been ruled “scientifically unacceptable” by Ruth Hubbard, an emeritus professor at the Harvard Biological Laboratories deeply skeptical about determinism. In his letter, Hamer writes, Lewontin

went on to theorize that human behaviors must be “very, very far from the genes” because “there are some at least that we know for sure are not influenced by genes as, for example, the particular language one speaks.” That made about as much sense as saying that since some people eat tacos and some eat hamburgers, there is no biological drive to eat.

Hamer, tongue firmly in cheek, offered to give Lewontin’s students a lecture on how good research into behavior genetics is done. Lewontin accepted. On the day of his scheduled talk, Hamer faced not only Lewontin but also Ruth Hubbard and Evan Balaban (a co-author of the hostile letter later published in Science). Hamer described his methods carefully and stressed that his research could identify only potential genetic influences and not isolate specific genetic causes of behavior. At the end of the lecture, Lewontin indicated that he had no dispute with Hamer after all, and left the classroom without further comment. One wonders from this if Lewontin has modified his views on studying genetic contributions to human behavior.

Although it is true that heritability is only a crude measure of genetic influence, it remains a valuable research tool if, as one scientist has said, the researchers realize that

genetic influence on behavior appears to involve multiple genes rather than one or two major genes, and nongenetic sources of variance are at least as important as genetic factors….This should not be interpreted to mean that genes do not affect human behavior; it only demonstrates that genetic influence on behavior is not due to major-gene effects.[18]

More importantly, one can move beyond the “lump sum” theory of genetic influences to study the way in which genes affect behavior over time, or to discover how a gene influences different but possibly related behaviors, for instance both sexual preference and aggression.

Lewontin also cited the “terrible mischief” that could result from a research program based on heritability as his reason to suggest stopping “the endless search for better methods of estimating useless quantities.”” Hamer agrees that precise genetic determinacy is an impossible goal; his 1993 article for Science on DNA markers also ended with an unusual admonition:

We believe that it would be fundamentally unethical to use [this] information to try to assess or alter a person’s current or future sexual orientation, either heterosexual or homosexual, or other normal attributes of human behavior. Rather, scientists, educators, policy-makers, and the public should work together to ensure that such research is used to benefit all members of society.

If scientists who have opposed research on heritability would accept that it can have, when it is carried out in this spirit, an important place in the study of behavior, that would add much-needed weight to calls to expand, and improve, research on human sexuality.

Although Hamer and LeVay have both expressed cautious confidence in their results, they are evidently uneasy about their own categorizations of men as either gay or straight. Hamer writes that,

In truth, I don’t think that there is such a thing as “the” rate of homosexuality in the population at large. It all depends on the definition, how it’s measured, and who is measured.

Classifying sexuality into homosexual and heterosexual categories may have benefits of simplicity for researchers, but how closely does this division fit the real world? Poorly is the answer. Sexual behavior and styles of life among men and women vary from day to day and year to year, and a conclusion about whether or not sexual experience is characterized as homosexual frequently depends on the definition one uses.[20] The slippery nature of our crude categories should alert us to beware of conclusions about groups labeled as “homosexual” or “heterosexual.”

Moreover, the concept of sexuality itself cannot easily be analyzed. It exists at several levels–chromosomal, genital, brain, preference, gender self-image, gender role, and a range of subtle influences on behavior (hair color, eye color, and many more). Each of these can be grouped together with the others to produce a single measurable component on a scale, devised by Alfred Kinsey in the 1940s, that allegedly shows a person’s degree of homosexual preference. Hamer used this scale somewhat uncritically to categorize his volunteers. Stephen Levine, a medical expert on sexual behavior, has noted that the conflated and crude Kinsey scale “does not do justice to the diversity among homosexual women and men.”[21]

One of Hamer’s severest critics, Anne Fausto-Sterling, a developmental geneticist at Brown University, has tried to extend sexual categories beyond the binary divisions of male and female[(22] She suggests adding three more groups based on “intersex” humans: herms (true hermaphrodites who possess one testis and one ovary), merms (individuals who have testes, no ovaries, but some female genitalia), and ferms (who have ovaries, no testes, but some male characteristics). This attempt to create multiple categories is, however, futile. It tries to systematize the un-systematizable by proposing a neatly divided-up continuum of sexuality, while, in fact, very different and mutually exclusive factors may be at work in particular cases. It is an impossible and intellectually misguided task.

Two major studies examining the historical origins of modern sexual categories show how social groupings that evolve over time can mislead one into supposing that inherent biological classes exist in some unchangeable sense. Michel Foucault chronicled the history of sexual norms by concentrating on the fluid notion of “homosexuality.”[23] He denounced what he called “Freud’s conformism” in taking heterosexuality to be the normal standard in psychoanalysis. He concluded:

We must not forget that the psychological, psychiatric, medical category of homosexuality was constituted from the moment it was characterized–Westphal’s famous article of 1870 on “contrary sexual sensations” can stand as its date of birth[24]–less by a type of sexual relations than by a certain quality of sexual sensibility…. The sodomite had been a temporary aberration; the homosexual was now a species.

This analysis, it seems to me, points to a critical error in the research of both Hamer and LeVay. Both, in spite of their qualifications, adopt the idea of the homosexual as a physical “species” different from the heterosexual. But there are no convincing historical grounds for this view. As Foucault points out, at the time of Plato,

People did not have the notion of two distinct appetites allotted to different individuals or at odds with each other in the same soul; rather, they saw two ways of enjoying one’s pleasure…

The cultural historian Jonathan Katz has recently attacked the naive partitioning of sexual orientation by tracing the dominance of the norm–heterosexuality –throughout history.[25] He provides a convincing argument that the “just-is hypothesis” of heterosexuality–i.e., that the word corresponds to a true behavioral norm–is an “invented tradition.” He shows that the categories of gay and straight are gradually dissolving as notions of the family become more various. Basing his view more on intuition than on sociological evidence, he predicts “the declining significance of sexual orientation.”

The final issue that has confused the interpretation of research into sexuality is the meaning of “biological influence.” Unfortunately, both LeVay and Hamer, in their effort to popularize their findings, ignore the subtlety of this question. As has been noted, LeVay is unambiguous about his own position on biological determinism,

The most promising area for exploration is the identification of genes that influence sexual behavior and the study of when, where, and how these genes exert their effects.

Both researchers ignore the central issue in the debate over nature and nurture. The question is: How do genes get you from a biochemical program that instructs cells to make proteins to an unpredictable interplay of behavioral impulses–fantasy, courtship, arousal, sexual selection–that constitutes “sexuality”? The question remains unresolved. The classic fall-back position is to claim that genes merely provide a basis, at most a predisposition, to a particular behavior. But such statements lack a precise or testable meaning.

Perhaps we are asking the wrong question when we set out to find whether there is a gene for sexual orientation. We know that genes are responsible for the development of our lungs, larynx, mouth, and the speech areas of our brain. And we understand that this complexity cannot be collapsed into the notion of a gene for “talking.” Similarly, what possible basis can there be for concluding that there is a single gene for sexuality, even though we accept that there are genes that direct the development of our penises, vaginas, and brains? This analogy is not to deny the importance of genes, but merely to recast their role in a different conceptual setting, one devoid of dualist prejudice.

The search for a single dominant gene–the “O-GOD” (one gene, one disorder) hypothesis–that would influence a behavioral variant is likely to be fruitless. Many different genes, together with many different environmental factors, will interact in unpredictable ways to guide behavioral preferences. Each component will contribute small quanta of influence. One result of such a quantum theory of behavior is that it makes irrelevant the overstretched speculations of both Hamer and LeVay about why a gene for homosexuality still exists when it apparently has little apparent survival value in evolutionary terms. The quest for a teleological explanation to identify a reason for the existence of a “gay gene” becomes pointless when one understands that there is not now, and never was, a single and final reason for being gay or straight, or having any other identity along the continuum of sexual preference.

Does this complexity, together with an adverse and polarized social milieu, preclude successful research efforts concerning human sexuality? In 1974, Lewontin wrote that reconstruction of man’s genetic past is “an activity of leisure rather than of necessity.”[26] Perhaps so. But, as Robert Plomin argues, the value of studying inheritance in behavior lies in its importance

per se rather than in its usefulness for revealing how genes work. Some of society’s most pressing problems, such as drug abuse, mental illness, and mental retardation, are behavioral problems. Behavior is also a key in health as well as illness, in abilities as well as disabilities, and in the personal pluses of life, such as sense of well-being and the ability to love and work.[27]

What research into human sexuality, then, lies ahead? Dean Hamer has repeated his initial work among male homosexuals in an entirely new group of families and has included a much-needed analysis of women. He has also compared the frequency of the Xq28 marker among pairs of gay siblings and their heterosexual brothers, important control data that he did not acquire the first time around. This work has been submitted to the journal Nature Genetics. Two other teams–one recently formed at the National Institutes of Health and a Canadian group that has reached some preliminary results–are attempting to replicate Hamer’s initial findings. All Hamer will say about his latest data is that they have not discouraged him from continuing with his project.

To track down and sequence the DNA from one or more relevant genes at Xq28, from a total of about two hundred candidates, seems an almost insuperable task. To read the molecular script of DNA involves deciphering millions of constituent elements. Moreover, each gene will have to be studied individually and many more pairs of gay brothers will be needed to achieve this goal. The work will be extremely difficult for a single laboratory to undertake on its own. Hamer’s request for a federally funded center for research into sexuality–a National Institute of Sexual Health–is therefore timely, for the study of differences between the sexes has reached a critical, though admittedly fragmented, stage and a coordinated research program would be valuable.

The concerns of such an institute should be broad. For example, it might have included the recent work reported from Yale which overturns the conventional view that language function is identical for both men and women.[28] By studying which brain areas were activated during various linguistic tasks, the Yale scientists found that women used regions in both their right and left brain cortices in certain instances, while men used only the left side of their brains. If functional brain differences for sophisticated behaviors exist between the sexes, the task for the future would be to link function to structure and to describe how both evolve from a background of genetic and environmental influence.

Inevitably, the idea of biological determinism carries with it the threat of manipulating the genes or the brain in order to adapt to the prevailing norm. As I have noted, Hamer was acutely aware of this possibility when he wrote his paper. But the prospects for pinpointing genetic risk have moved rapidly and worryingly forward with the recent availability of genetic screening techniques for, among other diseases, several cancers, including a small proportion of cancers of the breast, colon, and thyroid. Most such techniques are used without any current prospect for gene therapy or for any other effective treatment of the conditions identified. Geneticists such as Francis Collins, director of the Human Genome Project, have opposed unrestricted and unregulated screening techniques, describing their recent uses as “alarming”[29] because we are “treading into a territory which the genetics community has felt rather strongly is still [in the stage of] research.” Hamer’s fine words opposing genetic manipulation are likely to mean little in the marketplace if his work eventually leads to the isolation of a gene that has an effect on sexual preference, even if it has only a small effect that is present in only a limited number of people. US state legislatures are slowly responding to these issues. Colorado recently became the eleventh state to enact a law preventing information derived from genetic testing to be used in a discriminatory fashion.

In recognition of the emerging risks from dubious applications of preliminary discoveries, NIH launched a Task Force on Genetic Testing in April. The twenty-member committee includes representatives from industry, managed-care organizations, and patient-advocacy groups, and is chaired by Neil A. Holtzman, a professor of pediatrics and health policy at Johns Hopkins University. Far from being a friend to the hyperbolists, Holtzman has written that “physicians should be at the forefront of decrying florid genetic determinism and its dire implications for health and welfare reform.”[30] His committee is charged with performing a two-year study of genetic technologies, which will look specifically at the accuracy, safety, reliability, and social implications of new testing procedures. This move is not without self-interest on the part of the geneticists at the NIH. Members of the US Congressional House Appropriations Committee, which closely monitors NIH spending, have said that they may freeze the Human Genome Project’s $153 million grant if ethics issues are not given close attention.

But sex-based research has already run into political trouble. The Council for Citizens Against Government Waste has charged that some NIMH research is a misuse of taxpayer’s money. Tom Schatz, CCAGW’s president, has criticized twenty such studies, including one involving research into sex offenders. Rex Cowdry, acting director of the National Institute of Mental Health, argues that “for these grants, I think first you have to believe that the factors that motivate and control sexual behavior are worth knowing about…you have to believe that knowing more about how men and women are both similar and different is important.”[31]

With such partisan pressures dominating the future of the research agenda, the circulation of uninformed opinions couched in scholarly prose is a cause for anxiety. In an otherwise superb and iconoclastic critique of the history of heterosexuality, Jonathan Katz ends with a sweeping and badly informed declaration:

Biological determinism is misconceived intellectually, as well as politically loathsome…Contrary to today’s bio-belief, the heterosexual/homosexual binary is not in nature, but is socially constructed, therefore deconstructable.

LeVay and Hamer on the one hand, and Katz, on the other, evidently have taken completely antithetical positions. But Katz’s extreme intellectual reductionism makes him as guilty as the more simplistic biologists and journalists who inflate claims about every new genetic discovery. After convincingly undermining the distinction between gay and straight, he then accepts the naive dualism of nature vs. nurture. It is such attempts as Katz’s to put into opposition forces that are not in opposition which argue so strongly for planned research free from the ideological temptations that he succumbs to. Biological research into sexuality will indeed be misconceived if we assume that we already understand the differences between the sexes. In part the results of that research often contradict any such assumption. Katz demands that “we need to look less to oracles [presumably biological], and trust more in our desires, visions, and political organizing.” But to take this path risks perpetuating a debate based on ignorance rather than one based on evidence.

It is true that the research of Hamer and LeVay presents technical and conceptual difficulties and that their preliminary findings obviously need replication or refutation. Yet their work represents a genuine epistemological break away from the past’s rigid and withered conceptions of sexual preference. The pursuit of understanding about the origins of human sexuality –the quest to find an answer to the question, What does it mean to be gay and/or straight?–offers the possibility of eliminating what can be the most oppressive of cultural forces, the prejudiced social norm.

1 See Perversions: Psychodynamics and Therapy, edited by Sandor Lorand and Michael Balint (Ortolan Press, 1965; first edition, Random House, 1956), p. 75.

2 Quoted in Kenneth Lewes, The Psychoanalytic Theory of Male Homosexuality (Simon and Schuster, 1988), p. 188.

3 See Bernard J. Oliver, Jr., Sexual Deviation in American Society (College and University Press, 1967), p. 146.

4 See Karen de Witt, “Quayle Contends Homosexuality Is a Matter of Choice, Not Biology,” The New York Times, September 14, 1992, p. A17.

5 See Larry Thompson, “Search for a Gay Gene,” Time (June 12, 1995), pp. 60-61.

6 See Shang-Ding Zhang and Ward F. Odenwald, “Misexpression of the White (w) Gene Triggers Male-male Courtship in Drosophila,” Proceedings of the National Academy of Sciences, USA, Vol. 92 (June 6, 1995), pp. 5525-5529.

7 See Simon LeVay, “A Difference in Hypothalamic Structure Between Heterosexual and Homosexual Men,” Science (August 30, 1991), pp. 1034-1037.

8 The suprachiasmatic nucleus, also located in the hypothalamus, is larger in homosexual men than in either heterosexual men or women. The anterior commissure of the corpus callosum (a band of tissue that connects the right and left hemispheres of the brain) is also larger in gay men.

9 See Dean H. Hamer et al., “A Linkage Between DNA Markers on the X Chromosome and Male Sexual Orientation,” Science (July 16, 1993), pp. 321-327.

10. The normal complement of human chromosomes is forty-six per individual, two of which are designated sex chromosomes. In the male, the sex chromosomal makeup is XY, while in the female it is XX. If a gene for homosexuality (Xh) was transmitted through the maternal line, one can see how the subsequent offspring would be affected.

(Chart omitted)

Suppose the unaffected female carrier for homosexuality (XXh) produced offspring with a non-Xh male (XY). Half of all female children would be carriers of Xh (like their mothers), while half of all male offspring would carry Xh unopposed by another X. The Xh trait — homosexuality — would then be able to express itself.

11 By chance, one would expect each pair of brothers to share half their DNA. So, assuming that there was no gene for homosexuality, one would expect twenty of the forty pairs of brothers to share the X chromosome marker.

12 LeVay has recently completed a second book in collaboration with Elisabeth Nonas–City of Friends–that surveys gay and lesbian culture; it will be published by MIT Press in November. He is currently working on Queer Science, a study of how scientific research has affected the lives of gays and lesbians.

13 See Anne Fausto-Sterling and Evan Balaban, “Genetics and Male Sexual Orientation,” Science (September 3, 1993), p. 1257.

14 For example, see David Weatherall, Science and the Quiet Art (Norton, 1995) who notes that “these findings should not surprise us. Almost every condition…reveals a complex mixture of nature and nurture,” p. 287.

15 See R.C. Lewontin, S. Rose, and L. J. Kamin, Not in Our Genes (Pantheon, 1984).

16 Lewontin is not a total skeptic about the importance of molecular genetics research in medicine. For instance, he accepts “that some fraction of cancers arise on a background of genetic predisposition.” See R.C. Lewontin, “The Dream of the Human Genome,” The New York Review (May 28, 1992), pp. 31-40.

17 See M. W. Feldman and R. C. Lewontin, “The Heritability Hang-up,” Science (December 19, 1975), pp. 1163-1168.

18 See Robert Plomin, “The Role of Inheritance in Behavior,” Science (April 13, 1990), pp. 183-188.

19 See R.C. Lewontin, “The Analysis of Variance and the Analysis of Causes,” The American Journal of Human Genetics, Vol. 26 (1974), pp. 400-411.

20 For example, in a UK study (see Anne M. Johnson, “Sexual lifestyles and HIV risks,” Nature [December 3, 1992], pp. 410-412), although only 1.4 percent of men reported a male partner during the past five years, 6.1 percent of men reported having experienced some same-gender behavior.

21 See Stephen B Levine, Sexual Life: A Clinician’s Guide (Plenum, 1992). The Kinsey scale has seven levels ranging from exclusively heterosexual (0) to exclusively gay (6). Hamer applied this scale to four aspects of sexuality: self-identification, attraction, fantasy, and behavior.

22 See Anne Fausto-Sterling, “The Five Sexes: Why Male and Female Are Not Enough,” The Sciences (March/April, 1993), pp. 20-24.

23 See Michel Foucault, The History of Sexuality, Vols. One and Two (Vintage, 1990).

24 Dr. K.F.O. Westphal became the first modern author to publish an account of what he described as a “contrary sexual feeling” (Die contrare Sexualempfindung), although the word homosexual was first used in a private letter written by Karl Maria Kertbeny on May 6, 1868. This linguistic history is described in detail by Jonathan Katz (see note 25).

25 See Jonathan Ned Katz, The Invention of Heterosexuality (Dutton, 1995).

26 R.C. Lewontin, “The Analysis of Variance and the Analysis of Causes,” The American Journal of Human Genetics, Vol. 26 (1974), pp. 400-411.

27. Robert Plomin, “The Role of Inheritance in Behavior,” Science (April 13, 1990), pp. 183-188.

28. See Bennett A. Shaywitz et al., “Sex differences in the functional organization of the brain for language,” Nature (February 16, 1995), pp. 607-609.

29 See Gina Kolata, “Tests to Assess Risks for Cancer Raising Questions,” The New York Times (March 27, 1995), p. A1.

30 See Neil A. Holtzman, “Genetics,” Journal of the American Medical Association (April 26, 1995), pp. 1304-1306.

31 See “NIMH’s Cowdry Defends Institute’s Research Against Appropriations Committee, Watchdog Group Criticism,” The Blue Sheet (March 29, 1995), pp. 5-6.

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A gay Gene – Is Homosexuality Inherited Assault On Gay …

Nicole Kush Female Cannabis Seeds by DNA Genetics and …

Nicole Kush is the first new cannabis strain to be released by DNA Genetics in collaboration with Marimberos.

The sativa-dominant strain, Nicole, can trace it’s lineage back to a carefully bred plant in Mexico’s Durango desert almost ten years ago. With a pedigree that includes such classic strains as MK Ultra, Shiskaberry and Blueberry, Nicole was then crossed with DNA Genetics legendary Kosher Kush to create this exciting new strain – Nicole Kush.

DNA and Marimberos’ test grows of Nicole Kush, conducted in a legal environment, showed insane, over-the-top resin production. A blanket of sticky trichomes coats the plants; Nicole Kush is ideal for extractions. Flavours and aromas are fruity like blueberries and wine or even grape jam.

A lovely new strain from DNA and Marimberos that is a certainty to be popular with connoisseur cannabis seed collectors everywhere.

PROMO LIVE NOW Purchase any seed from DNA Genetics Family and Receive 2 Free Seeds of Sour Diesel (Fem)

All our descriptions and images have come direct from the breeders who operate in a legal climate much different to that within the United Kingdom. Take note, you should NEVER try cultivating any cannabis plants within ANY jurisdiction where such cultivation is illegal. Our seeds are sold purely for souvenirs and should be treated as a curio or novelty item and should never be germinated. PLEASE DO NOT BREAK THE LAW!

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Nicole Kush Female Cannabis Seeds by DNA Genetics and …

Genetics – X Linked Problems – The Biology Corner


**In fruit flies, eye color is a sex linked trait. Red is dominant to white.**

1. What are the sexes and eye colors of flies with the following genotypes?

X R X r _________ X R Y __________ X r X r __________

X R X R ____________ X r Y ____________

2. What are the genotypes of these flies:

white eyed, male ____________ red eyed female (heterozygous) ________

white eyed, female ___________ red eyed, male ___________

3. Show the cross of a white eyed female X r X r with a red-eyed male X R Y .

4. Show a cross between a pure red eyed female and a white eyed male. What are the genotypes of the parents:

___________ and _______________

How many are:

white eyed, male ____ white eyed, female ____ red eyed, male ____ red eyed, female ____

5. Show the cross of a red eyed female (heterozygous) and a red eyed male.

What are the genotypes of the parents?

___________ & ________________

How many are:

white eyed, male ____ white eyed, female ____ red eyed, male ____ red eyed, female ____

Math: What if in the above cross, 100 males were produced and 200 females. How many total red-eyed flies would there be? ________

6. In humans, hemophilia is a sex linked trait. Females can be normal, carriers, or have the disease. Males will either have the disease or not (but they wont ever be carriers)

X h Y= male, hemophiliac

Show the cross of a man who has hemophilia with a woman who is a carrier.

What is the probability that their children will have the disease? __________

7. A woman who is a carrier marries a normal man. Show the cross. What is the probability that their children will have hemophilia? What sex will a child in the family with hemophilia be?

8. A woman who has hemophilia marries a normal man. How many of their children will have hemophilia, and what is their sex?

9. In cats, the gene for calico (multicolored) cats is codominant. Females that receive a B and an R gene have black and oRange splotches on white coats. Males can only be black or orange, but never calico.

Heres what a calico females genotype would look like: X B X R

Show the cross of a female calico cat with a black male?

What percentage of the kittens will be black and male? _________ What percentage of the kittens will be calico and male? _________ What percentage of the kittens will be calico and female? _________

10. Show the cross of a female black cat, with a male orange cat.

What percentage of the kittens will be calico and female? _____What color will all the male cats be? ______

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Genetics – X Linked Problems – The Biology Corner

Genetics and Inheritance – National Fragile X Foundation

What Are Chromosomes?

Our bodies are made up of about 60 trillion cells. Each one of those cells manufactures proteins. The kinds of proteins any given cell makes determine its particular characteristics, which in turn create the characteristics of the entire body.

The instructions for making these proteins are stored in chemicals or molecules called DNA, which is organized into chromosomes. Chromosomes are found in the center, or nucleus, of all of our cells, including the eggs and sperm.

Female Chromosomes

Male Chromosomes

Chromosomes are passed down from generation to generation through the egg and sperm. Typically, we all have 46 chromosomes in our cells, two of which are sex chromosomes. In females, these are two Xs; in males they are an X and a Y.

Genes are sections of DNA that are passed from generation to generation and perform one function. If we think of DNA as letters in the alphabet, the genes are words and the chromosome is a full sentence. All 46 chromosomes then make up the whole book.

There are many genes on each chromosome; we all have tens of thousands of genes that instruct our bodies on how to develop.

Genes are given names to identify them and the gene responsible for fragile X syndrome is called FMR1. The FMR1 Gene is on the X chromosome.

The FMR1 gene appears in four forms that are defined by the number of repeats of a pattern of DNA called CGG repeats.

Individuals with less than 45 CGG repeats have a normal FMR1 gene. Those with 45-54 CGG repeats have what is called an intermediate or grey zone allele, which does not cause any of the known fragile X associated disorders.

Individuals with 55-200 CGG repeats have a premutation, which means they carry an unstable mutation of the gene that can expand in future generations and thus cause fragile X syndrome in their children or grandchildren. Individuals with a premutation can also develop FXTAS or FXPOI themselves.

Individuals with over 200 CGG repeats have a full mutation of the FMR1 gene, which causes fragile X syndrome.

The full mutation causes the FMR1 gene to shut down or methylate in one region. Normally, the FMR1 gene produces an important protein called FMRP. When the gene is turned off, the individual does not make this protein. The lack of this specific protein is what causes fragile X syndrome.

Fragile X-associated Disorders are a group of conditions called trinucleotide repeat disorders. A common feature of these conditions is that the gene can change sizes over generations, becoming more unstable, and thus the conditions may occur more frequently or severely in subsequent generations. These conditions are often caused by a gene change that begins with a premutation and then expands to a full mutation in subsequent generations.

Approximately 1 in 151 females and 1 in 468 males carry the FMR1 premutation. They are thus carriers of the premutation.

Premutations are defined as having 55-200 CGG repeats and can occur in both males and females. When a father passes the premutation on to his daughters, it usually does not expand to a full mutation. A man never passes the fragile X gene to his sons, since he passes only his Y chromosome to them, which does not contain a fragile X gene.

A female with the FMR1 premutation will often pass on a larger version of the mutation to her children (more on this point below). She also has a 50 percent chance of passing on her normal X chromosome in each pregnancy, since usually only one of her X chromosomes has the FMR1 mutation.

The chance of the premutation expanding to a full mutation is related to the size of the mothers premutation. The larger the mothers CGG repeat number, the higher the chance that it will expand to a full mutation if it is passed on.

Typically, the premutation has no immediate and observable impact on a persons appearance or health. However, some females with a premutation will experience fragile X-associated primary ovarian insufficiency (FXPOI), which causes infertility, irregular or missed menstrual cycles, and/or early menopause.

Additionally, some older adults with a premutation may develop a neurological condition called FXTAS, (fragile X-associated tremor/ataxia syndrome), an adult onset neurodegenerative disorder.

FXTAS and FXPOI are part of the family of conditions called Fragile X-associated Disorders.

A full mutation is defined as having over 200 CGG repeats and causes that indicate the presence of fragile X syndrome in males and some females. Most full mutation expansions have some degree of Methylation (the process which turns off the gene). Males with a full mutation will have Fragile X Syndrome, though with varying degrees of severity

About 65-70 percent of females with a full mutation exhibit some difficulties with cognitive, learning, behavioral, or social functioning, and may also have some of the physical features of FXS (such as large ears or a long face). The remaining 30-35 percent are at risk to develop mental health issues such as anxiety or depression, or they may have no observable effects of the full mutation.

Fragile X in an X-linked condition, which means that the gene is on the X chromosome.

Since a woman has two X chromosomes a woman with a premutation or full mutation has a 50% chance of passing on the X with the mutation in each pregnancy, and a 50% chance of passing on her normal X.

If she has a premutation, and it is passed on (to either males or females), it can remain a premutation or it can expand to a full mutation. If she has a full mutation and it is passed on (to either males or females), it will remain a full mutation.

Because males have only one X chromosome, fathers who carry the premutation will pass it on to all their daughters and none of their sons (they pass their Y chromosome on to their sons). There have been no reports of premutations that are passed from a father to his daughter expanding to a full mutation. This appears to only occur when passed from a mother to her children.

In many X-linked conditions only males who inherit the abnormal gene are affected. Fragile X syndrome is one of the X-linked conditions that can also affect females.

Additionally, in other X-linked conditions all males who carry the abnormal form of the gene are affected. In fragile X syndrome, unaffected males can carry the gene in the premutation form while themselves having no symptoms of the condition.

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Genetics and Inheritance – National Fragile X Foundation

Molecular Genetics Laboratory of Female Reproductive Cancer

The long-term objectives of our research team are:

a. to understand the molecular etiology in the development of human cancer, and b. to identify and characterize cancer molecules for cancer detection, diagnosis, and therapy.

We use ovarian carcinoma as a disease model because it is one of the most aggressive neoplastic diseases in women. For the first research direction, we aim to identify and characterize the molecular alterations during initiation and progression of ovarian carcinomas. Previous genome-wide analyses from our team have identified molecular alterations in several new cancer-associated genes including Rsf-1, NAC-1, and Notch3 among several others. We have demonstrated the essential roles of these gene products in sustaining tumor growth and survival. Current projects are focusing on elucidating the mechanisms by which these genes function in cancer cells and delineating the cross-talks between those genes and other signaling pathways. Specifically, we are identifying their downstream targets and pathways, and are determining their roles in maintaining cancer stem cell-like features, invasion and drug resistance. The second research direction is a translation-based study. We are assessing the clinical significance of an array of new cancer-associated genes in predicting clinical outcome and in the developing potential target-based therapy in mouse preclinical models. We are also establishing innovative assays for cancer detection and diagnosis by identifying new tumor-associated genetic and protein biomarkers through serial analysis of gene expression, gene expression arrays, proteomics and methylation profiling. The purpose is to develop new tools in detecting human cancer using body fluid samples. In collaboration with several investigators, we are integrating new technologic platforms such as microfluidics, nanotechnology and systems biology in our studies.

In addition to ovarian cancer genetics, we are interested in the diagnostic pathology and basic research of gestational trophoblastic diseases. Please visit “Pathology of Trophoblastic Lesions” for details.

Click here for the Ovarian Cancer Prevention Website

Click here for the Ovarian Cancer Research Program

“What we observe is not nature itself, but nature exposed to our method of questioning.” — Werner Heisenberg, Physics and Philosophy, 1958

Tian-Li Wang, PhD

Professor Departments of Pathology, Oncology, and Gynecology & Obstetrics Faculty in Pathobiology Graduate Program Johns Hopkins Medical Institutions

National Taiwan University, BS Johns Hopkins University School of Medicine, PhD University of Pennsylvania, School of Medicine, Post-doc fellow (Neuroscience) Howard Hughes Medical Institutions, Associate (Cancer Genetics)

Ie-Ming Shih, MD, PhD Co-director, Breast & Ovarian Cancer Program Sidney Kimmel Comprehensive Cancer Center

Richard W. TeLinde Professor Department of Gynecology & Obstetrics Departments of Pathology and Oncology Faculty in Pathobiology Graduate Program Johns Hopkins University School of Medicine

Taipei Medical University, MD University of Pennsylvania, PhD Johns Hopkins University, Residency (Pathology) Johns Hopkins University, Fellowships (Gynecologic Pathology and Cancer Genetics)

See more here:
Molecular Genetics Laboratory of Female Reproductive Cancer

Y chromosome – Wikipedia, the free encyclopedia

The Y chromosome is one of two sex chromosomes (allosomes) in mammals, including humans, and many other animals. The other is the X chromosome. Y is the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction. In mammals, the Y chromosome contains the gene SRY, which triggers testis development. The DNA in the human Y chromosome is composed of about 59 million base pairs.[2] The Y chromosome is passed only from father to son. With a 30% difference between humans and chimpanzees, the Y chromosome is one of the fastest evolving parts of the human genome.[3] To date, over 200 Y-linked genes have been identified.[4] All Y-linked genes are expressed and (apart from duplicated genes) hemizygous (present on only one chromosome) except in the cases of aneuploidy such as XYY syndrome or XXYY syndrome. (See Y linkage.)

The Y chromosome was identified as a sex-determining chromosome by Nettie Stevens at Bryn Mawr College in 1905 during a study of the mealworm Tenebrio molitor. Edmund Beecher Wilson independently discovered the same mechanisms the same year. Stevens proposed that chromosomes always existed in pairs and that the Y chromosome was the pair of the X chromosome discovered in 1890 by Hermann Henking. She realized that the previous idea of Clarence Erwin McClung, that the X chromosome determines sex, was wrong and that sex determination is, in fact, due to the presence or absence of the Y chromosome. Stevens named the chromosome “Y” simply to follow on from Henking’s “X” alphabetically.[5][6]

The idea that the Y chromosome was named after its similarity in appearance to the letter “Y” is mistaken. All chromosomes normally appear as an amorphous blob under the microscope and only take on a well-defined shape during mitosis. This shape is vaguely X-shaped for all chromosomes. It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.[7]

Most mammals have only one pair of sex chromosomes in each cell. Males have one Y chromosome and one X chromosome, while females have two X chromosomes. In mammals, the Y chromosome contains a gene, SRY, which triggers embryonic development as a male. The Y chromosomes of humans and other mammals also contain other genes needed for normal sperm production.

There are exceptions, however. For example, the platypus relies on an XY sex-determination system based on five pairs of chromosomes.[8] Platypus sex chromosomes in fact appear to bear a much stronger homology (similarity) with the avian Z chromosome,[9] and the SRY gene so central to sex-determination in most other mammals is apparently not involved in platypus sex-determination.[10] Among humans, some men have two Xs and a Y (“XXY”, see Klinefelter syndrome), or one X and two Ys (see XYY syndrome), and some women have three Xs or a single X instead of a double X (“X0”, see Turner syndrome). There are other exceptions in which SRY is damaged (leading to an XY female), or copied to the X (leading to an XX male). For related phenomena, see Androgen insensitivity syndrome and Intersex.

Many ectothermic vertebrates have no sex chromosomes. If they have different sexes, sex is determined environmentally rather than genetically. For some of them, especially reptiles, sex depends on the incubation temperature; others are hermaphroditic (meaning they contain both male and female gametes in the same individual).

The X and Y chromosomes are thought to have evolved from a pair of identical chromosomes,[11][12] termed autosomes, when an ancestral mammal developed an allelic variation, a so-called ‘sex locus’ simply possessing this allele caused the organism to be male.[13] The chromosome with this allele became the Y chromosome, while the other member of the pair became the X chromosome. Over time, genes which were beneficial for males and harmful to (or had no effect on) females either developed on the Y chromosome, or were acquired through the process of translocation.[14]

Until recently, the X and Y chromosomes were thought to have diverged around 300 million years ago. However, research published in 2010,[15] and particularly research published in 2008 documenting the sequencing of the platypus genome,[9] has suggested that the XY sex-determination system would not have been present more than 166 million years ago, at the split of the monotremes from other mammals.[10] This re-estimation of the age of the therian XY system is based on the finding that sequences that are on the X chromosomes of marsupials and eutherian mammals are present on the autosomes of platypus and birds.[10] The older estimate was based on erroneous reports that the platypus X chromosomes contained these sequences.[8][16]

Recombination between the X and Y chromosomes proved harmfulit resulted in males without necessary genes formerly found on the Y chromosome, and females with unnecessary or even harmful genes previously only found on the Y chromosome. As a result, genes beneficial to males accumulated near the sex-determining genes, and recombination in this region was suppressed in order to preserve this male specific region.[13] Over time, the Y chromosome changed in such a way as to inhibit the areas around the sex determining genes from recombining at all with the X chromosome. As a result of this process, 95% of the human Y chromosome is unable to recombine. Only the tips of the Y and X chromosomes recombine. The tips of the Y chromosome that could recombine with the X chromosome are referred to as the pseudoautosomal region. The rest of the Y chromosome is passed on to the next generation intact. It is because of this disregard for the rules that the Y chromosome is such a superb tool for investigating recent human evolution from a male perspective.

By one estimate, the human Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence, and linear extrapolation of this 1,393-gene loss over 300 million years gives a rate of genetic loss of 4.6 genes per million years.[17] Continued loss of genes at the 4.6 genes per million year rate would result in a Y chromosome with no functional genes that is the Y chromosome would lose complete function within the next 10 million years, or half that time with the current age estimate of 160 million years.[13][18] Comparative genomic analysis reveals that many mammalian species are experiencing a similar loss of function in their heterozygous sex chromosome. Degeneration may simply be the fate of all non-recombining sex chromosomes, due to three common evolutionary forces: high mutation rate, inefficient selection, and genetic drift.[13]

However, comparisons of the human and chimpanzee Y chromosomes (first published in 2005) show that the human Y chromosome has not lost any genes since the divergence of humans and chimpanzees between 67 million years ago,[19] and a scientific report in 2012 stated that only one gene had been lost since humans diverged from the rhesus macaque 25 million years ago.[20] These facts provide direct evidence that the linear extrapolation model is flawed and suggest that the current human Y chromosome is either no longer shrinking or is shrinking at a much slower rate than the 4.6 genes per million years estimated by the linear extrapolation model.

The human Y chromosome is particularly exposed to high mutation rates due to the environment in which it is housed. The Y chromosome is passed exclusively through sperm, which undergo multiple cell divisions during gametogenesis. Each cellular division provides further opportunity to accumulate base pair mutations. Additionally, sperm are stored in the highly oxidative environment of the testis, which encourages further mutation. These two conditions combined put the Y chromosome at a greater risk of mutation than the rest of the genome.[13] The increased mutation risk for the Y chromosome is reported by Graves as a factor 4.8.[13] However, her original reference obtains this number for the relative mutation rates in male and female germ lines for the lineage leading to humans.[21]

Without the ability to recombine during meiosis, the Y chromosome is unable to expose individual alleles to natural selection. Deleterious alleles are allowed to “hitchhike” with beneficial neighbors, thus propagating maladapted alleles in to the next generation. Conversely, advantageous alleles may be selected against if they are surrounded by harmful alleles (background selection). Due to this inability to sort through its gene content, the Y chromosome is particularly prone to the accumulation of “junk” DNA. Massive accumulations of retrotransposable elements are scattered throughout the Y.[13] The random insertion of DNA segments often disrupts encoded gene sequences and renders them nonfunctional. However, the Y chromosome has no way of weeding out these “jumping genes”. Without the ability to isolate alleles, selection cannot effectively act upon them.

A clear, quantitative indication of this inefficiency is the entropy rate of the Y chromosome. Whereas all other chromosomes in the human genome have entropy rates of 1.51.9 bits per nucleotide (compared to the theoretical maximum of exactly 2 for no redundancy), the Y chromosome’s entropy rate is only 0.84.[22] This means the Y chromosome has a much lower information content relative to its overall length; it is more redundant.

Even if a well adapted Y chromosome manages to maintain genetic activity by avoiding mutation accumulation, there is no guarantee it will be passed down to the next generation. The population size of the Y chromosome is inherently limited to 1/4 that of autosomes: diploid organisms contain two copies of autosomal chromosomes while only half the population contains 1 Y chromosome. Thus, genetic drift is an exceptionally strong force acting upon the Y chromosome. Through sheer random assortment, an adult male may never pass on his Y chromosome if he only has female offspring. Thus, although a male may have a well adapted Y chromosome free of excessive mutation, it may never make it in to the next gene pool.[13] The repeat random loss of well-adapted Y chromosomes, coupled with the tendency of the Y chromosome to evolve to have more deleterious mutations rather than less for reasons described above, contributes to the species-wide degeneration of Y chromosomes through Muller’s ratchet.[23]

As it has been already mentioned, the Y chromosome is unable to recombine during meiosis like the other human chromosomes; however, in 2003, researchers from MIT discovered a process which may slow down the process of degradation. They found that human Y chromosome is able to “recombine” with itself, using palindrome base pair sequences.[24] Such a “recombination” is called gene conversion.

In the case of the Y chromosomes, the palindromes are not noncoding DNA; these strings of bases contain functioning genes important for male fertility. Most of the sequence pairs are greater than 99.97% identical. The extensive use of gene conversion may play a role in the ability of the Y chromosome to edit out genetic mistakes and maintain the integrity of the relatively few genes it carries. In other words, since the Y chromosome is single, it has duplicates of its genes on itself instead of having a second, homologous, chromosome. When errors occur, it can use other parts of itself as a template to correct them.

Findings were confirmed by comparing similar regions of the Y chromosome in humans to the Y chromosomes of chimpanzees, bonobos and gorillas. The comparison demonstrated that the same phenomenon of gene conversion appeared to be at work more than 5 million years ago, when humans and the non-human primates diverged from each other.

In the terminal stages of the degeneration of the Y chromosome, other chromosomes increasingly take over genes and functions formerly associated with it. Finally, the Y chromosome disappears entirely, and a new sex-determining system arises.[13] Several species of rodent in the sister families Muridae and Cricetidae have reached these stages,[25][26] in the following ways:

Outside of the rodent family, the black muntjac, Muntiacus crinifrons, evolved new X and Y chromosomes through fusions of the ancestral sex chromosomes and autosomes.[32]

Fisher’s principle outlines why almost all species using sexual reproduction have a sex ratio of 1:1, meaning that 50% of offspring will receive a Y chromosome, and 50% will not. W.D. Hamilton gave the following basic explanation in his 1967 paper on “Extraordinary sex ratios”,[33] given the condition that males and females cost equal amounts to produce:

In humans, the Y chromosome spans about 58 million base pairs (the building blocks of DNA) and represents approximately 1% of the total DNA in a male cell.[34] The human Y chromosome contains over 200 genes, at least 72 of which code for proteins.[2] Traits that are inherited via the Y chromosome are called holandric traits (although biologists will usually just say ‘Y-linked’).

Some cells, especially in older men and smokers, lack a Y-chromosome. It has been found that men with a higher percentage of hematopoietic stem cells in blood lacking the Y-chromosome (and perhaps a higher percentage of other cells lacking it) have a higher risk of certain cancers and have a shorter life expectancy. Men with “loss of Y” (which was defined as no Y in at least 18% of their hematopoietic cells) have been found to die 5.5 years earlier on average than others. This has been interpreted as a sign that the Y-chromosome plays a role going beyond sex determination and reproduction[35] (although the loss of Y may be an effect rather than a cause). And yet women, who have no Y-chromosome, have lower rates of cancer. Male smokers have between 1.5 and 2 times the risk of non-respiratory cancers as female smokers.[36][37]

The human Y chromosome is normally unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres (which comprise about 5% of the chromosome’s length). These regions are relics of ancient homology between the X and Y chromosomes. The bulk of the Y chromosome, which does not recombine, is called the “NRY” or non-recombining region of the Y chromosome.[38] It is the SNPs (single-nucleotide polymorphism) in this region that are used to trace direct paternal ancestral lines.

Not including pseudoautosomal genes, genes include:

Y-Chromosome-linked diseases can be of more common types, or very rare ones. Yet, the rare ones still have importance in understanding the function of the Y-chromosome in the normal case.

No vital genes reside only on the Y chromosome, since roughly half of humans (females) do not have a Y chromosome. The only well-defined human disease linked to a defect on the Y chromosome is defective testicular development (due to deletion or deleterious mutation of SRY). However, having two X chromosomes and one Y chromosome has similar effects. On the other hand, having Y chromosome polysomy has other effects than masculinization.

Y chromosome microdeletion (YCM) is a family of genetic disorders caused by missing genes in the Y chromosome. Many affected men exhibit no symptoms and lead normal lives. However, YCM is also known to be present in a significant number of men with reduced fertility or reduced sperm count.

This results in the person presenting a female phenotype (i.e., is born with female-like genitalia) even though that person possesses an XY karyotype. The lack of the second X results in infertility. In other words, viewed from the opposite direction, the person goes through defeminization but fails to complete masculinization.

The cause can be seen as an incomplete Y chromosome: the usual karyotype in these cases is 44X, plus a fragment of Y. This usually results in defective testicular development, such that the infant may or may not have fully formed male genitalia internally or externally. The full range of ambiguity of structure may occur, especially if mosaicism is present. When the Y fragment is minimal and nonfunctional, the child is usually a girl with the features of Turner syndrome or mixed gonadal dysgenesis.

Klinefelter syndrome (47, XXY) is not an aneuploidy of the Y chromosome, but a condition of having an extra X chromosome, which usually results in defective postnatal testicular function. The mechanism is not fully understood; the extra X does not seem to be due to direct interference with expression of Y genes.

47,XYY syndrome (simply known as XYY syndrome) is caused by the presence of a single extra copy of the Y chromosome in each of a male’s cells. 47, XYY males have one X chromosome and two Y chromosomes, for a total of 47 chromosomes per cell. Researchers have found that an extra copy of the Y chromosome is associated with increased stature and an increased incidence of learning problems in some boys and men, but the effects are variable, often minimal, and the vast majority do not know their karyotype. When chromosome surveys were done in the mid-1960s in British secure hospitals for the developmentally disabled, a higher than expected number of patients were found to have an extra Y chromosome. The patients were mischaracterized as aggressive and criminal, so that for a while an extra Y chromosome was believed to predispose a boy to antisocial behavior (and was dubbed the ‘criminal karyotype’). Subsequently, in 1968 in Scotland the only ever comprehensive nationwide chromosome survey of prisons found no over-representation of 47,XYY men, and later studies found 47,XYY boys and men had the same rate of criminal convictions as 46,XY boys and men of equal intelligence. Thus, the “criminal karyotype” concept is inaccurate and obsolete.[citation needed]

The following Y chromosome-linked diseases are rare, but notable because of their elucidating of the nature of the Y chromosome.

Greater degrees of Y chromosome polysomy (having more than one extra copy of the Y chromosome in every cell, e.g., XYYY) are rare. The extra genetic material in these cases can lead to skeletal abnormalities, decreased IQ, and delayed development, but the severity features of these conditions are variable.

XX male syndrome occurs when there has been a recombination in the formation of the male gametes, causing the SRY-portion of the Y chromosome to move to the X chromosome. When such an X chromosome contributes to the child, the development will lead to a male, because of the SRY gene.

In human genetic genealogy (the application of genetics to traditional genealogy), use of the information contained in the Y chromosome is of particular interest because, unlike other chromosomes, the Y chromosome is passed exclusively from father to son, on the patrilineal line. Mitochondrial DNA, maternally inherited to both sons and daughters, is used in an analogous way to trace the matrilineal line.

Research is currently investigating whether male-pattern neural development is a direct consequence of Y chromosome-related gene expression or an indirect result of Y chromosome-related androgenic hormone production.[39]

The presence of male chromosomes in fetal cells in the blood circulation of women was discovered in 1974.[40] In 1996, it was found that male fetal progenitor cells could persist postpartum in the maternal blood stream for as long as 27 years.[41]

A 2004 study at the Fred Hutchinson Cancer Research Center, Seattle investigated the origin of male chromosomes found in the peripheral blood of women who had not had male progeny. A total of 120 subjects (women who had never had sons) were investigated and it was found that 21% of them had male DNA. The subjects were categorised into four groups based on their case histories:[42]

The study noted that 10% of the women had never been pregnant before, raising the question where the Y Chromosomes in their blood could have come from? The study suggests that possible reasons for occurrence of male chromosome microchimerism could be one of the following:[42]

A 2012 study, at the same institute, has detected cells with the Y chromosome in multiple areas of the brains of dead women.[43]

Many groups of organisms in addition to mammals have Y chromosomes, but these Y chromosomes do not share common ancestry with mammalian Y chromosomes. Such groups include Drosophila, some other insects, some fish, some reptiles, and some plants. In Drosophila melanogaster, the Y chromosome does not trigger male development. Instead, sex is determined by the number of X chromosomes. The D. melanogaster Y chromosome does contain genes necessary for male fertility. So XXY D. melanogaster are female, and D. melanogaster with a single X (X0), are male but sterile. There are some species of Drosophila in which X0 males are both viable and fertile.

Other organisms have mirror image sex chromosomes: the female is “XY” and the male is “XX”, but by convention biologists call a “female Y” a W chromosome and the other a Z chromosome. For example, female birds, snakes, and butterflies have ZW sex chromosomes, and males have ZZ sex chromosomes.

There are some species, such as the Japanese rice fish, where the Y chromosome is not inverted and can still swap genes with the X. Because the Y does not have male-specific genes and can interact with the X, XX males can be formed as well as XY and YY females.[44]

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Y chromosome – Wikipedia, the free encyclopedia

Davis Angus Foss, Oklahoma

Value Genetics Bull & Female Sale

Saturday March 5, 2016 12:30 p.m. Clinton Livestock Auction, Clinton, OK View Sale Book View Videos

Davis Angus began in 1973 when Bud Davis, Jim’s father purchased ten registered Angus cows from Al Rutledge. Jim and wife Debbie, later added cattle from the UT, Allen Greer and Pat O’Brian, and B&L dispersals. The first AI sires were introduced in 1995; Davis Angus chose BR New Design 323 and TC Dividend 963. Through the technological advances of breeding and the use of artificial insemination inspiration developed, a dream that cattle could be produced that had all the desired carcass traits with the show ring appeal. This idea led Davis Angus to produce the cattle you see today. Cattle that have Carcass and Conformation without Compromise.

The 2007 Davis Angus calf crop was very successful with 100% of the steers grading choice, 60% went CAB and prime, producing a 46% yield grade 1 and 2, this allowed Davis Angus to receive a premium of $106.95 per head above the market while costing only $0.78 per pound with corn costing $6.00 per bushel.

Davis Angus was very successful in the show ring with several champions; we encourage you to view our “Hall of Champions” page and view the results!

In the past decade we have become very successful in the show ring as well as winning several carcass competitions.

We encourage you to come visit us at Davis Angus, let us put you in the winner’s circle!

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Davis Angus Foss, Oklahoma

X chromosome – Wikipedia, the free encyclopedia

The X chromosome is one of the two sex-determining chromosomes (allosomes) in many animal species, including mammals (the other is the Y chromosome), and is found in both males and females. It is a part of the XY sex-determination system and X0 sex-determination system. The X chromosome was named for its unique properties by early researchers, which resulted in the naming of its counterpart Y chromosome, for the next letter in the alphabet, after it was discovered later.[2]

The X chromosome in humans spans more than 153 million base pairs (the building material of DNA). It represents about 2000 out of 20,000 – 25,000 genes. Each person normally has one pair of sex chromosomes in each cell. Females have two X chromosomes, whereas males have one X and one Y chromosome. Both males and females retain one of their mother’s X chromosomes, and females retain their second X chromosome from their father. Since the father retains his X chromosome from his mother, a human female has one X chromosome from her paternal grandmother (father’s side), and one X chromosome from her mother.

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 contains about 2000[3] genes compared to the Y chromosome containing 78[4] genes, out of the estimated 20,000 to 25,000 total genes in the human genome. Genetic disorders that are due to mutations in genes on the X chromosome are described as X linked.

The X chromosome carries a couple of thousand genes but few, if any, of these have anything to do directly with sex determination. Early in embryonic development in females, one of the two X chromosomes is randomly and permanently inactivated in nearly all somatic cells (cells other than egg and sperm cells). This phenomenon is called X-inactivation or Lyonization, and creates a Barr body. If X-inactivation in the somatic cell meant a complete de-functionalizing of one of the X-chromosomes, it would ensure that females, like males, had only one functional copy of the X chromosome in each somatic cell. This was previously assumed to be the case. However, recent research suggests that the Barr body may be more biologically active than was previously supposed.[5]

It is theorized by Ross et al. 2005 and Ohno 1967 that the X chromosome is at least partially derived from the autosomal (non-sex-related) genome of other mammals, evidenced from interspecies genomic sequence alignments.

The X chromosome is notably larger and has a more active euchromatin region than its Y chromosome counterpart. Further comparison of the X and Y reveal regions of homology between the two. However, the corresponding region in the Y appears far shorter and lacks regions that are conserved in the X throughout primate species, implying a genetic degeneration for Y in that region. Because males have only one X chromosome, they are more likely to have an X chromosome-related disease.

It is estimated that about 10% of the genes encoded by the X chromosome are associated with a family of “CT” genes, so named because they encode for markers found in both tumor cells (in cancer patients) as well as in the human testis (in healthy patients).[6]

Klinefelter syndrome:

Triple X syndrome (also called 47,XXX or trisomy X):

Turner syndrome:

XX male syndrome is a rare disorder, where the SRY region of the Y chromosome has recombined to be located on one of the X chromosomes. As a result, the XX combination after fertilization has the same effect as a XY combination, resulting in a male. However, the other genes of the X chromosome cause feminization as well.

X-linked endothelial corneal dystrophy is an extremely rare disease of cornea associated with Xq25 region. Lisch epithelial corneal dystrophy is associated with Xp22.3.

Megalocornea 1 is associated with Xq21.3-q22[medical citation needed]

The X-chromosome has played a crucial role in the development of sexually selected characteristics for over 300 million years. During that time it has accumulated a disproportionate number of genes concerned with mental functions. For reasons that are not yet understood, there is an excess proportion of genes on the X-chromosome that are associated with the development of intelligence, with no obvious links to other significant biological functions.[11][12] There has also been interest in the possibility that haploin sufficiency for one or more X-linked genes has a specific impact on development of the Amygdala and its connections with cortical centres involved in socialcognition processing or the social brain’.[11][13][clarification needed]

It was first noted that the X chromosome was special in 1890 by Hermann Henking in Leipzig. Henking was studying the testicles of Pyrrhocoris and noticed that one chromosome did not take part in meiosis. Chromosomes are so named because of their ability to take up staining. Although the X chromosome could be stained just as well as the others, Henking was unsure whether it was a different class of object and consequently named it X element,[14] which later became X chromosome after it was established that it was indeed a chromosome.[15]

The idea that the X chromosome was named after its similarity to the letter “X” is mistaken. All chromosomes normally appear as an amorphous blob under the microscope and only take on a well defined shape during mitosis. This shape is vaguely X-shaped for all chromosomes. It is entirely coincidental that the Y chromosome, during mitosis, has two very short branches which can look merged under the microscope and appear as the descender of a Y-shape.[16]

It was first suggested that the X chromosome was involved in sex determination by Clarence Erwin McClung in 1901 after comparing his work on locusts with Henking’s and others. McClung noted that only half the sperm received an X chromosome. He called this chromosome an accessory chromosome and insisted, correctly, that it was a proper chromosome, and theorized, incorrectly, that it was the male determining chromosome.[14]

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X chromosome – Wikipedia, the free encyclopedia

Human Genetics – Mendelian Inheritance 5


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.

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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



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.

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

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Female Infertility Genetic Causes | RSC New Jersey

Female Hereditary Hair Loss Treatment & Genetic Testing … – 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

To learn more about Hair Restoration Physician, Dr. Alan J. Bauman, M.D. visit

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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.

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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.


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

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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