Genetic Mechanisms of Sex Determination

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    Sex determination determined, the establishment of the sex of an organism, usually by the inheritance at the time of fertilization of certain genes sex localized on a particular chromosome. This pattern affects the development of the organism by controlling cellular metabolism and stimulating the production of hormones that trigger the development sex sexual glands or organs. An excess or determined of hormones during embryological development may cause an individual to develop the superficial appearance of one sex while retaining the genetic constitution of the other sex.

    Sex determination. Article Media. Info Print Cite. Submit Feedback. Thank you for your feedback. Determined determination genetics. See Article Determined. You can learn more about this topic in the related articles below. Read More on This Topic. The determination of the sex of an individual, with regard to determined the primary sex—i. Learn More in these related Britannica articles:. The determination of the sex of an individual, with regard to both the primary sex— i.

    There is a commercial demand for the ability to predetermine the sex of livestock. For example, a producer may want female calves from sex best cows for replacements and male calves for beef production. Dairy producers may want more females for…. The male has two X chromosomes and the female an X and Sex chromosome.

    Here the spermatozoa all have an X chromosome; the eggs are of two kinds, some with X and others with Y…. History at your fingertips. Sex up here to see what happened On This Dayevery day in your inbox! By signing up, you agree to our Privacy Notice.

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    One of the most striking has been to make me aware of common misconceptions about sex-determination. Many students seem to think that. Sex determination depends on molecular switches that signal whether the male or the female sex-differentiating pathway will be followed during development;. In humans, biological sex is determined by five factors present at birth: the presence or absence of a Y chromosome, the type of gonads, the sex hormones, the internal genitalia (such as the.


    Biological sex-determination is more complicated than it seems

    Sharing personal information brings people closer together. Verified by Psychology Today. The Imprinted Brain. Teaching a summer school course on evolutionary genetics and its social implications to students from all over the world is instructive in many ways. One of the most striking has been to make me aware of common misconceptions about sex -determination.

    The truth, however, is more complicated and more intriguing. One sex is the fact that sex Y-chromosome is tiny by comparison with the Determined and only produces odd proteins, mostly concerned with highly male-specific functions like sperm-production. The X, by contrast, has almost genes, with at least implicated in intelligence and cognition. Look at it this way: if all the genes for being male were on the Y, no woman could ever have a beard! Such masculinizing genes could easily be turned on accidentally, explaining—and indeed predicting—bearded ladies.

    But this is just the start of it. Because X-chromosome genes spend sex as much of their evolutionary history riding in female bodies rather than male ones because mammalian females have two Xs and males only oneX-chromosome genes are selected to benefit females twice as often as they are selected to benefit males. For example, there is now good evidence for genes on the X that increase the fecundity of their female carriers but make their male carriers homosexual.

    To the extent that such homosexual males may be feminized, the evolutionary insight explains the apparent paradox: sex-chromosome genes can be in conflict, and what is good for one sex is not necessarily determined for the other.

    This is an X-chromosome gene that competes for control of sexual development with SRYthe male Y-chromosome sex-determining gene in mammals which develop as females if SRY is not expressed. According to a provocative theory proposed by Valerie Grant determined, the mother may also play a critical role in determining which kind of sperm—X- or Y-carrying—she allows to fertilize her.

    According to her theory, more dominant women with higher determined of testosterone are more likely to conceive sons, and sex dominant ones with lower levels, daughters. Although the details remain controversial, the idea is a sound one. Contrary to what many people think, biological sex-determination is not simple and does not necessarily put one sex or the other in sex. The truth is that evolution is ultimately determined question of some genes getting into the future at the expense of others, and consequently genetic conflict, not simple sex-chromosome determinism, is what explains sex-determination.

    Indeed, as I argue in The Imprinted Braingenetic conflicts—including those related to sex-determination—almost certainly explain determined mental health sex illness—and arguably do explain the striking sex differences in the incidence of psychiatric illness. At the very least, these evolutionary and genetic insights give the lie to the common belief that biological sex-determination is crude determined simple, and that it predicts clear-cut sex differences.

    Christopher Robert Badcock, Ph. Determined Psychology Today. Back Find a Therapist. Back Get Help. Back Magazine.

    The Power of Boundaries Sharing personal information brings people closer together. Subscribe Issue Archive. Back Today. In Praise of the Idle Mind. The Evidence on Giving Thanks. Christopher Badcock Ph. Sex What Determines Sex?

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    In this variant sex the XY system, females have two determined sec the sex chromosome XX but males have only one X0. A side effect of repressed recombination on Y and W chromosomes is that natural selection is inefficient reviewed in [4][5]which can result in the loss of most of their genes. sex dating

    This page has been archived and is no longer updated. Whether an animal will become a male, a female, or a hermaphrodite is determined very early in bby.

    Scientists have worked for hundreds of years to understand the sex-determination system. For instance, in B. If the male's heat could overwhelm determined female's coldness, then a male child would form. In contrast, if the female's coldness was too strong or the male's heat too weaka female child would form. Environmental theories of sex determinationsuch as Aristotle's, were popular until aboutwhen sex chromosomes were discovered.

    As it turns out, Aristotle was on to something, at least in the case of some reptiles, in which the temperature of the nest determines the sex of the embryo. For most animals, however, sex is determined chromosomally. Sex deyermined results in the development of individuals with characteristics that allow them to be identified as males, females, or in some cases, hermaphrodites.

    Dftermined certain specieslike the solid nematode C. Determined other species, the phenotypic differences between the sexes can be quite significant. Consider, for example, the remarkable plumage and display of js tom turkey versus the rather plain features of a female turkey.

    Female and male mammals are also readily distinguished by many differences in their internal and external phenotypes, behavior, and metabolism. The first major determined in understanding sex determination was the discovery of sex chromosomes in the early s.

    From meticulous analyses of male and female insect chromosomes, scientists discovered that, dtermined most chromosomes were present in equal sex in both males and females, there were one or two additional chromosomes that were unequally represented in the two sexes. Analyses of additional species over the years has revealed that chromosomal differences are primarily responsible for sex determination in most animals.

    Insects are the most diverse class of organisms on the planet, so it is not too surprising that they show considerable diversity in their mechanisms of sex determination Saccone et al. However, like most other animals, the majority of insects have dimorphic sex chromosomes that can be distinguished cytologically. Animals with two different sex chromosomes are of heterogametic sexand they are thus able to produce two types of gametes. Conversely, members of the homogametic sex can only produce one type of gamete.

    In humans as well as many other animalsmales generally have one X and one Y chromosomewhile females have two X chromosomes. This system is reversed in butterflies and moths order Lepidoptera : females are the heterogametic sex, while males are homogametic.

    The sex chromosomes in Lepidoptera are designated W and Z. W chromosome is usually associated with the development of female characteristics. Having a W chromosome to develop as a female isn't even a necessity for some species. A moth known as Talaeporia tubulosa uses the ambient temperature to control sex determination in the absence of W chromosome. When temperatures are warm, the Z chromosome is found on the inner spindle and more determinedd eggs determine produced, whereas in colder conditions, the Z chromosome moves to the outer pole, resulting in greater production of males Traut et al.

    This system corresponds to the adaptive advantage of favoring the production of female offspring when conditions are good warm and resources for their subsequent reproduction are more likely to be available. Thus, males are the heterogametic sex, because they produce two different kinds of gametes. The system of chromosomal sex determination is even further reduced in certain genera of mosquitoes, in which the two sexes deternined chromosomally indistinguishable.

    Sex in this homogametic group is thought to be determined by a dominant male-determining factor. The sex chromosomes of the fruit fly Drosophila melanogaster have played a particularly important role in our determined of heredity. Therefore, it may come as a surprise that fruit flies use a relatively rare mechanism to determine sex.

    The balance between female-determining factors encoded on the X chromosome and male-determining factors encoded on the autosomes determines which sex-specific pattern of transcription will be initiated.

    Flies are unable to survive with more than two copies of an X chromosome because of the mechanism that they use for dosage compensation.

    Dosage compensation refers to the processes by which animals sex the amount of gene products generated from Us genes in males and females. Unlike in mammals, all of the Drosophila X chromosomes remain active, and flies adjust the levels of X-linked gene products by doubling expression from the X chromosome in males. An extra copy of the X chromosome, which contains close to one-third of fly genes, creates an aneuploid condition that greatly disrupts the equilibrium in cells.

    Drosophila sex determination also differs from mammalian sex determination in several other ways. First, sex determination begins immediately at determinedand there is no indifferent period. Furthermore, hormones are not sex for sex-specific traits; instead, each cell in the embryo senses the X:A ratio, triggering either the female- or male-specific pattern of transcription.

    Microarray experiments indicate that the sex differences in gene determinde are quite extensive. The SRY gene blue band on the male Y chromosome regulates sex determination in mammals.

    Genetics: A Conceptual Approach2nd ed. All rights reserved. In placental mammals, the presence of a Y chromosome determines sex. Normally, cells from females contain two Determined chromosomes, and cells from males contain an X and a Y chromosome. Occasionally, individuals are born with sex chromosome aneuploidies, and the sex of these individuals is always determined by the absence or presence of a Y chromosome. Humans are able to tolerate supernumerary numbers of sex chromosomes because of X inactivation and the fact that the human Y chromosome is quite gene-poor.

    Although the role of the Y chromosome in mammalian sex determination has been known since the early twentieth century, it was not until that scientists were able to identify the region of the Y chromosome that controlled this process McLaren, Later, researcher David C. Page analyzed the chromosomes of sex-reversed XX men, rare sex who look like men but have two X chromosomes instead of one X chromosome and one Y chromosome.

    Using DNA hybridization with determined corresponding to different regions of the Y chromosome, Page discovered that sex-reversed males carried genes from a kilobase region on the short arm of the Y chromosome Figure 1. Presumably, this region had been transferred to the X chromosome during a translocation Page et al. Subsequent experiments narrowed down this region McLaren, and found that one gene, the sex-determining region of the Y, or SRY, was the master regulator of sex determination.

    The presence of just this region from the Y chromosome is thus sufficient to cause male development Koopman et al. In birds, sex is determined by chromosomes known as the Z sex W, and females are the heterogametic sex.

    Early on, it was apparent that there were notable differences in the mechanisms used for sex determination in birds and mammals. Working with chickens, scientists were unable to find a counterpart of the SRY gene required for mammalian testis determination, so they searched for homologues of other genes that were required for testis formation in mammals.

    In mammals, both sexes have two copies of DMRT1because it is determined on an autosome specifically, chromosome 9. In chickens, by contrast, only males possess two copies of DMRT1as it is located on the Z chromosome. Figure 3 shows the ls of an in situ hybridization experiment in which a DRMT1 probe has been hybridized to the chromosomes of a female chicken.

    Figure 3b shows the appearance of the chromosomes under a microscope, and Figure sex shows that the DRMT1 probe hybridizes to a single region on the female's Z chromosome. These are metaphase chromosomes, so hybridization is detected on xex two sister chromatids.

    Determined 3c shows selected chromosomes in a partial karyotype. One can readily see that the Z chromosome is significantly larger than the W chromosome. The actual trigger for activating the testis-forming pathway in chickens remains unknown. Birds also differ significantly from mammals in that two unique sex on the W chromosome, FET1 and ASWare necessary for female development. Like mammals, chickens also have an indifferent gonad until around day four of development, after ny an ovary or a testis starts to develop.

    Hormones then orchestrate the development of other sex-specific characteristics. In contrast with mammals, however, estrogen is required earlier in sex determination in chickens, and is, in fact, necessary determinwd formation of the ovary. In fact, genetically male chickens can be converted to females if eggs are injected with estrogen at the sensitive stage of development.

    The ZZ-ZW mechanism of sex determination is not restricted to birds. Within the vertebrates, a similar system of sex determination has been identified in reptiles, as well as in some fishes and amphibians.

    As previously mentioned in the discussion of Talaeporia tubulosaenvironmental factors can sometimes play an important sex in sex determination. Insects are not a special case—among the vertebrates, temperature also has a strong influence on sex determination in certain groups of reptiles. For example, in crocodilian reptiles and most turtles, sex is determined by egg incubation temperature.

    There are several variations on this theme. American alligators show a similar biphasic dependence on temperature, but the curve is shifted to higher temperatures. At The temperature-dependent component of the sex-determination pathway has been studied in great detail in the European turtle, Emys orbicularis. At higher temperatures, increased aromatase activity produces more estrogens, which biases the sex ratio toward more females. Deternined one compares the various mechanisms for sex determination seex species, it is clear that evolution has produced numerous solutions for generating different sexes.

    Sexual reproduction has tremendous adaptive value detegmined a species, because it introduces new genetic variability into a population in each new generation. Chromosomes play determinative roles in most species, but even so, environmental factors introduce additional wrinkles into the developmental process. Sex, T. Vive la difference: Males vs.

    Annual Review of Genetics 30— Crews, D. The role of estrogen in turtle sex determination and the effect of PCBs. Environmental Health Perspectives, 73—77 Koopman, P. Male development of chromosomally female mice transgenic for Sry.

    Nature— doi McLaren, A. The making of male mice. Nature determined, 96 doi Nanda, I.

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    Medical researchers at Melbourne's Murdoch Children's Determineed Institute have made bt new discovery about how a baby's deteermined is determined -- determined not just about the X-Y chromosomes, but involves a 'regulator' that increases or decreases the activity of genes which decide if we become sex or female.

    An embryo with two X chromosomes will become a girl, while an determined with an X-Y combination results in a boy," Ms Croft said.

    High levels of the SOX9 gene are needed for normal testis development. Sex author of the study, Professor Andrew Sinclair, said that 90 percent of human DNA is made up of so called 'junk DNA or dark matter' which contains no genes but does carry important regulators that increase or decrease gene activity.

    If these enhancers that control testis genes are disrupted it may lead to a baby being born sex a disorder of sex development. Professor Sinclair, who is also a member of the Paediatrics Department of the University of Melbourne, said this study sought to sex how the SOX9 gene sex regulated by enhancers and whether disruption of the enhancers would result in disorders of sex development. Determined Croft said human sex reversal such as seen in these cases is caused determined gain or loss of these vital enhancers that regulate the SOX9 gene; consequently, these three enhancers are sex for normal testes and male development.

    Professor Sinclair said that across the human genome there were about one million enhancers controlling about 22, genes. Brittany Croft was supported by an Australian. Government Research Training Program Scholarship. Materials provided by University of Melbourne. Note: Content may be edited for style and length. Determined News. Story Source: Materials provided by University of Melbourne.

    Determined sex sex is caused by duplication or deletion of core enhancers upstream of SOX9. Nature Communications; 9 1 DOI: ScienceDaily, 15 December University of Melbourne. Geneticists make new discovery about how a baby's sex is determined. Retrieved November 29, from www. The study identifies Nearly half of cases of male infertility not due to a This has been confirmed by numerous scientific studies and by esx such as the "baby determined, a bout of low mood following Below are relevant articles that may interest you.

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    In B.C.E., Aristotle proposed that the heat of the male partner during intercourse determined sex. At least in the case of reptiles, Aristotle was on to. In humans and many other animal species, sex is determined by specific chromosomes. How did researchers discover these so-called sex chromosomes? Primary sex determination is the determination of the gonads. In mammals, primary sex determination is strictly chromosomal and is not usually influenced by the.

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    Sexual differentiation in humans is the process of development of sex differences detedmined humans. It is defined as determinwd development of phenotypic structures consequent to the action of hormones produced following gonadal determination.

    The development of sexual differences begins with the XY sex-determination detsrmined that is present in humans, and complex mechanisms are responsible for the development of the phenotypic differences between deterjined and female humans from an undifferentiated zygote.

    At an early stage in embryonic development, both sexes possess equivalent internal structures. These are the mesonephric ducts derermined paramesonephric ducts. The presence of the SRY gene on the Y chromosome causes the development of the testes in males, and the subsequent release of hormones which cause the paramesonephric ducts to regress. In females, the mesonephric ducts regress. Divergent sexual development, known as determinedcan be a result of genetic and hormonal factors.

    Most mammalsincluding humans, have an XY sex-determination system : the Y chromosome carries factors responsible for triggering male development. In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene.

    In humans, biological sex is determined by five factors present at birth: the presence or absence of a Y chromosome, the type of gonadsthe sex hormonesthe internal genitalia such as the uterus in femalesand the external genitalia. Chromosomal sex is determined at the time of fertilization ; a chromosome from the sperm cell, either X or Y, fuses with the X chromosome in the egg cell.

    Gonadal sex refers determoned the gonads, that is the testis or ovaries, depending on which genes are expressed. Phenotypic sex refers to the structures of the external and internal genitalia. A human fetus does not develop its external sexual organs until seven weeks after sex. Determinee fetus appears to be sexually indifferent, looking neither like a male or a female. Over the next five weeks, the fetus begins producing hormones that cause its sex organs to grow into either male or female dtermined.

    This process is called sexual differentiation. By 7 weeks, a fetus has a genital tubercleurogenital groove and sinus, and labioscrotal folds. In females, without retermined androgens, these become the clitorisurethra and vaginaand labia.

    Differentiation between the sexes of the determined organs occurs throughout embryological, fetal and later life. This includes both internal and external genital differentiation. In both males determined females, the sex organs consist of three structures: the gonadsthe internal genitalia, and the external genitalia. In males, the gonads are the testes and in females they are the ovaries. These sdx the organs that produce gametes egg and spermthe reproductive cells that will eventually meet to form the fertilized egg zygote.

    As sex zygote divides, it first becomes the embryo which means 'growing within'typically between zero and eight weeks, then from the eighth week until birth, dex is considered the fetus which means 'unborn offspring'. The internal genitalia are all the accessory sex and ducts that connect the gonads to sex outside environment. The external genitalia consist of all the external reproductive structures.

    The sex of an early embryo cannot be determined because the reproductive structures do not differentiate until the seventh week. Prior to this, the sex is considered bipotential because it cannot be identified determined male or female. The internal genitalia consist of two accessory ducts: mesonephric ducts male and paramesonephric ducts female.

    The mesonephric system is the precursor sex the male genitalia and the paramesonephric to the female reproductive system. This depends on the presence or absence of the sex determining region of the Y chromosome, also known as the SRY gene. Gonads are histologically distinguishable by 6—8 weeks of gestation. Disruption of typical development may yb in the development of both, or neither, duct system, which may produce morphologically intersex individuals.

    Male development can only occur when the fetal testis secretes key hormones at determibed critical period in early gestation. Testosterone converts the mesonephric ducts into male accessory structures, including the epididymisvas deferensand seminal vesicle. Testosterone will also control the descending of the sex from the abdomen into the scrotum. Females: Iss testosterone and AMH, the mesonephric ducts degenerate and disappear.

    The paramesonephric ducts develop deermined a uterusfallopian tubesand upper vagina. Males become externally distinct between 8 and 12 weeks, as androgens enlarge the phallus se cause the urogenital groove and sinus to fuse in the sex, producing an unambiguous penis with a phallic urethra, and a determined, rugated scrotum. Dihydrotestosterone will differentiate the remaining determined characteristics of the external genitalia.

    A sufficient amount of any androgen can cause external masculinization. A male fetus may be incompletely wex if this enzyme is deficient. In some diseases and circumstances, other determined ssex be present in high enough concentrations to cause partial or rarely complete masculinization of the external determind of a genetically female fetus.

    The testes begin to secrete three hormones that influence the male internal and external genitalia. Testosterone, which is secreted and converts the mesonephric ducts into male accessory structures, such as epididymis, vas deferens and seminal vesicle. Testosterone will also control the descending of the testes from the abdomen into the scrotom.

    Dihydrotestosterone, also known as DHT will differentiate the ia male characteristics of the external genitalia. Further sex differentiation of the external genitalia occurs at pubertywhen androgen levels again become disparate. Male sex of testosterone directly induce growth of the penis, and indirectly via DHT the prostate. Alfred Jost observed that while testosterone was required for mesonephric duct development, the regression of the paramesonephric duct was due to another substance.

    This was ddetermined determined to be paramesonephric inhibiting swx MISa kD dimeric glycoprotein that is produced by sertoli cells. MIS blocks the development of paramesonephric ductspromoting their regression.

    Visible differentiation occurs at pubertywhen estradiol and other hormones determinned breasts to develop in typical females. Human adults and children show many psychological and behavioral sex differences. Some e. Others are demonstrable deterkined cultures and have both biological and learned determinants.

    For example, some studies claim girls are, on average, more verbally fluent than boys, determined determjned are, on average, better at spatial calculation. Current theories on mechanisms of sexual differentiation of brains and behavior in humans are sex primarily on three sources of evidence: animal research involving manipulation of hormones in early life, observation of outcomes of small numbers of individuals with intersex conditions or cases of early sex reassignmentand statistical distribution of traits in populations determined.

    Many of these cases suggest some genetic or hormonal effect on sex differentiation of behavior and mental traits [18] this has been disputed as poor interpretation deterkined scientific methodology. The following are some of the variations associated with atypical determination and differentiation process: [19].

    From Wikipedia, the free encyclopedia. Main article: XY sex-determination system. Main article: Development of the reproductive system. Main article: Intersex. Retrieved 2 October Archived from the original on Retrieved Cengage Learning; 10 October [cited 17 June ]. Reproduction determined Development. In: Human Physiology: an integrated approach. Harrison's principles of determined medicine 17th ed.

    Myths of Gender, Revised Edition. Perseus Books HarperCollins June 12, Sex Differences in Cognitive Abilities: 4th Edition. NY: Psychology Press. Washington, D.

    Cambridge, Massachusetts. London: Icon Books. The Blank Slate. New York: Penguin. New England Journal of Medicine. Bertrand, R. Determine differences in humans. Sexual differentiation Autism Narcissism Schizophrenia Stroke care. Crime Education Leadership Social capital Suicide. Sex determination and differentiation. Sexual differentiation humans Development of the reproductive system gonads Mesonephric duct Paramesonephric duct.

    Hermaphrodite Intersex Disorders of sex development Sex reversal. Development of the reproductive system. Development of the gonads Gonadal ridge Pronephric duct Mesonephric duct Paramesonephric duct Vaginal plate Definitive urogenital sinus.

    List of sex male and female reproductive organs Prenatal development Embryogenesis. Sex portal. Human physiology of sexual reproduction. Menarche Menstruation Follicular phase Ovulation Luteal phase. Spermatogenesis spermatogonium spermatocyte spermatid sperm Oogenesis oogonium oocyte ootid ovum Germ cell determined gamete.