Animals sex chromosomes

In humans and many other animal species, sex is determined by specific chromosomes. How did researchers discover these so-called sex chromosomes? The path from the initial discovery of sex chromosomes in 1891 to an understanding of their true function was paved by the diligent efforts of multiple scientists over the course of many years. As often happens during a lengthy course of discovery, scientists observed and described sex chromosomes long before they knew their function. By the 1880s, scientists had established methods for staining chromosomes so that they could be easily visualized using a simple light microscope. With this staining method, scientists were able to observe cell division and to identify the steps that occurred during both mitosis and meiosis (Figure 1). The first indication that sex chromosomes were distinct from other chromosomes came from experiments conducted by German biologist Hermann Henking in 1891. While using a light microscope to study sperm formation in wasps, Henking noticed that some wasp sperm cells had 12 chromosomes, while others had only 11 chromosomes. Also, during his observation of the stages of meiosis leading up to the formation of these sperm cells, Henking noticed that the mysterious twelfth chromosome looked and behaved differently than the other 11 chromosomes. Accordingly, he named the twelfth chromosome the "X element" to represent its unknown nature. Interestingly, when Henking used a light microscope to study egg formati...

• v • t • e The XY sex-determination system is a In humans, the presence of the Y chromosome is responsible for triggering male development; in the absence of the Y chromosome, the fetus will undergo female development. There are various exceptions, such as individuals with The XY system contrasts in several ways with the A Mechanisms [ ] All Mammals [ ] In most mammals, sex is determined by presence of the Y chromosome. This makes individuals with In the 1930s, SRY is a sex-determining gene on the Y chromosome in the [ citation needed] Not all male-specific genes are located on the Humans [ ] Main article: Whilst XY sex determination is the most familiar, since it is the system that humans use, there are a range of alternative systems found in nature. The inverse of the XY system (called Many insects of the order haplo-diploid system, where the females are full Influences [ ] Genetic [ ] In an interview for the Rediscovering Biology website, For a long time we thought that SRY would activate a cascade of male genes. It turns out that the sex determination pathway is probably more complicated and SRY may in fact inhibit some anti-male genes. The idea is instead of having a simplistic mechanism by which you have pro-male genes going all the way to make a male, in fact there is a solid balance between pro-male genes and anti-male genes and if there is a little too much of anti-male genes, there may be a female born and if there is a little too much of pro-male genes then the...

Whether an animal will become a male, a female, or a hermaphrodite is determined very early in development. Scientists have worked for hundreds of years to understand the sex-determination system. For instance, in 335 B.C.E., Aristotle proposed that the heat of the male partner during intercourse determined sex. If the male's heat could overwhelm the 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 weak), a female child would form. Environmental theories of sex determination, such as Aristotle's, were popular until about 1900, when sex chromosomeswere 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 determination results in the development of individuals with characteristics that allow them to be identified as males, females, or in some cases, hermaphrodites. In certain species, like the solid nematode C. elegans, differences in sexual characteristics can be very small; in fact, in C. elegans, the only distinguishing sexual characteristic is the presence of a testis versus an ovotestis. In other species, the phenotypic differences between the sexes can be quite significant. Consider, for example, the remarkable plumage and display of a tom turkey versus the rather plain features of a female turkey. Female and male m...

Sex determination of the gonads is important for development of the sex phenotype (internal and external genitalia, secondary characteristics) and sexual behavior. A sex chromosome genotype of XY leads to the development of testes due to the sex-determining region of the Y chromosome ( SRY) gene. The SRY gene induces downstream factors such as SRY-box containing gene 9 ( SOX9), anti-Müllerian hormone, and glial cell line–derived neurotrophic factor in Sertoli cells. Intersex conditions have been described in several domestic animal species. True hermaphrodites are rare and have both ovarian and testicular tissue and exhibit anomalies of the external genitalia. The karyotype is variable and may be a chimera, mosaic, or unknown. Pseudohermaphroditism, often referred to as sex reversal syndrome, is more common. Animals have one or the other type of gonad and external genitalia of the opposite sex. Animals may be XY SRY negative or XX SRY negative. In horses, the most common type is 64XY SRY negative. Some cases of sex reversal are believed to be due to a recessive autosomal gene mutation. The most common intersex condition, the male pseudohermaphrodite, has testicular tissue in the abdominal cavity or beneath the skin in the scrotal region, and external genital organs that resemble those of females. Miniature Schnauzers, Basset Hounds, and rarely, Persian cats may present with pseudohermaphroditism when affected by persistent paramesonephric (Müllerian) duct syndrome. Undesce...

\( \newcommand\) • • • • • • • • • • • • • The nuclei of human cells contain 22 autosomes and 2 sex chromosomes. In females, the sex chromosomes are the 2 X chromosomes. Males have one X chromosome and one Y chromosome. The presence of the Y chromosome is decisive for unleashing the developmental program that leads to a baby boy. The Y Chromosome In making sperm by meiosis, the X and Y chromosomes must separate in anaphase just as homologous autosomes do. This occurs without a problem because, like homologous autosomes, the X and Y chromosome synapse during prophase of meiosis I. There is a small region of homology shared by the X and Y chromosome and synapsis occurs at that region. Figure 7.6.1 Synapsis of the X and Y chromosomes courtesy of C. Tease This image, shows synapsis of the X and Y chromosomes of a mouse during prophase of meiosis I. Crossing over occurs in two regions of pairing, called the pseudoautosomal regions. These are located at opposite ends of the chromosome. The Pseudoautosomal Regions The pseudoautosomal regions get their name because any genes located within them (so far only 9 have been found) are inherited just like any autosomal genes. Males have two copies of these genes: one in the pseudoautosomal region of their Y, the other in the corresponding portion of their X chromosome. So males can inherit an allele originally present on the X chromosome of their father and females can inherit an allele originally present on the Y chromosome of their fa...

• Alemannisch • العربية • বাংলা • Bân-lâm-gú • Беларуская • Беларуская (тарашкевіца) • Bosanski • Català • Čeština • Dansk • Deutsch • Eesti • Ελληνικά • Español • فارسی • Français • Gaeilge • Galego • 한국어 • Íslenska • Italiano • עברית • Кыргызча • Magyar • Македонски • Nederlands • 日本語 • Norsk bokmål • Norsk nynorsk • Oʻzbekcha / ўзбекча • Polski • Português • Română • Русский • Simple English • کوردی • Српски / srpski • Suomi • Svenska • தமிழ் • ไทย • Türkçe • Українська • Tiếng Việt • 文言 • 粵語 • 中文 See also: All However, a small percentage of humans have a divergent sexual development, known as [ citation needed] It could also result from exposure, often in utero, to chemicals that disrupt the normal conversion of the allosomes into sex hormones and further into the development of either There is a gene in the Y chromosome that has regulatory sequences that control genes that code for maleness, called the Other vertebrates [ ] Diverse mechanisms are involved in the determination of sex in animals. Plants [ ] Many scientists argue that sex determination in plants is more complex than that in humans. This is because even Plant sex chromosomes are most common in M. polymorpha. The high prevalence of Sequence composition and evolution [ ] Amplification of transposable elements, S. latifolia sex chromosomes. S. latifolia. Silene species. This would conclude that microsatellites do not participate in Y-chromosome evolution. The portion of Y-chromosome that never recombine with...

hermaphroditism, the condition of having both male and female reproductive organs. Hermaphroditic In humans, conditions that involve discrepancies between external genitalia and internal reproductive organs are described by the term intersex. Intersex conditions are sometimes also referred to as disorders of sexual development (DSDs). Such conditions are extremely rare in humans. In ovotesticular disorder (sometimes also called true hermaphroditism), an individual has both ovarian and testicular Individuals with a 46,XX chromosome complement usually have

\( \newcommand\) • • • • • • • • • • • • • The nuclei of human cells contain 22 autosomes and 2 sex chromosomes. In females, the sex chromosomes are the 2 X chromosomes. Males have one X chromosome and one Y chromosome. The presence of the Y chromosome is decisive for unleashing the developmental program that leads to a baby boy. The Y Chromosome In making sperm by meiosis, the X and Y chromosomes must separate in anaphase just as homologous autosomes do. This occurs without a problem because, like homologous autosomes, the X and Y chromosome synapse during prophase of meiosis I. There is a small region of homology shared by the X and Y chromosome and synapsis occurs at that region. Figure 7.6.1 Synapsis of the X and Y chromosomes courtesy of C. Tease This image, shows synapsis of the X and Y chromosomes of a mouse during prophase of meiosis I. Crossing over occurs in two regions of pairing, called the pseudoautosomal regions. These are located at opposite ends of the chromosome. The Pseudoautosomal Regions The pseudoautosomal regions get their name because any genes located within them (so far only 9 have been found) are inherited just like any autosomal genes. Males have two copies of these genes: one in the pseudoautosomal region of their Y, the other in the corresponding portion of their X chromosome. So males can inherit an allele originally present on the X chromosome of their father and females can inherit an allele originally present on the Y chromosome of their fa...

Sex determination of the gonads is important for development of the sex phenotype (internal and external genitalia, secondary characteristics) and sexual behavior. A sex chromosome genotype of XY leads to the development of testes due to the sex-determining region of the Y chromosome ( SRY) gene. The SRY gene induces downstream factors such as SRY-box containing gene 9 ( SOX9), anti-Müllerian hormone, and glial cell line–derived neurotrophic factor in Sertoli cells. Intersex conditions have been described in several domestic animal species. True hermaphrodites are rare and have both ovarian and testicular tissue and exhibit anomalies of the external genitalia. The karyotype is variable and may be a chimera, mosaic, or unknown. Pseudohermaphroditism, often referred to as sex reversal syndrome, is more common. Animals have one or the other type of gonad and external genitalia of the opposite sex. Animals may be XY SRY negative or XX SRY negative. In horses, the most common type is 64XY SRY negative. Some cases of sex reversal are believed to be due to a recessive autosomal gene mutation. The most common intersex condition, the male pseudohermaphrodite, has testicular tissue in the abdominal cavity or beneath the skin in the scrotal region, and external genital organs that resemble those of females. Miniature Schnauzers, Basset Hounds, and rarely, Persian cats may present with pseudohermaphroditism when affected by persistent paramesonephric (Müllerian) duct syndrome. Undesce...

hermaphroditism, the condition of having both male and female reproductive organs. Hermaphroditic In humans, conditions that involve discrepancies between external genitalia and internal reproductive organs are described by the term intersex. Intersex conditions are sometimes also referred to as disorders of sexual development (DSDs). Such conditions are extremely rare in humans. In ovotesticular disorder (sometimes also called true hermaphroditism), an individual has both ovarian and testicular Individuals with a 46,XX chromosome complement usually have