Whether an animal will become a male, a female, or a hermaphrodite is determined very early in development. Aristotle proposed that, 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 were popular until about 1900, when sex chromosomes were discovered.?The environmental theories are true 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.
In placental mammals, the presence of a Y chromosome determines sex. Normally, cells from female gametes or eggs contain two X chromosomes (homogametic), and cells from male gametes or sperms contain an X and a Y chromosome (heterogametic). If a sperm cell containing an X chromosome fertilizes an egg, the resulting zygote will be XX or female. If the sperm cell contains a Y chromosome, then the resulting zygote will be XY or male
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. Thus, individuals with 47,XXY and 47,XYY karyotypes are males, while individuals with 45,X and 47,XXX karyotypes are females. 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.
MOLECULAR MECHANISM OF SEX DETERMINATION
In human embryos, the SRY gene encodes a unique transcription factor that activates a testis-forming pathway at about week seven of development. Before this time, the embryonic gonad is "indifferent," meaning that it is capable of developing into either a testis or an ovary Likewise, the early embryo has two systems of ducts, Wolffian and M?llerian ducts, which are capable of developing into the male and female reproductive tracts, respectively. Once the SRY gene product stimulates the indifferent gonad to develop into a testis, the testis begins producing two hormones, testosterone and anti-Mullerian hormone, or AMH. Testosterone and one of its derivatives, dihydrotestosterone, induce formation of other organs in the male reproductive system, while AMH causes the degeneration of the Mullerian duct. In females, who do not contain the SRY protein, the ovary-forming pathway is activated by a different set of proteins. The fully developed ovary then produces estrogen, which triggers development of the uterus, oviducts, and cervix from the Mullerian duct.
Figure shows the involvement of chromosomes in sex determination
This study was conducted with an aim to establish a relationship between sex and fingerprint ridge density. The fingerprints were taken from 500 subjects (250 males and 250 females) in the age group of 18-60 years. After taking fingerprints, the ridges were counted in the upper portion of the radial border of each print for all ten fingers and mean value was calculated. The results have shown that a finger print ridge of [less than or equal to] 13 ridges/25 [mm.sup.2] is more likely of male origin and finger print ridge of [greater than or equal to] 14 ridges/25 [mm.sup.2] is more likely of female origin. It has been successful to support the hypothesis that women tend to have a statistically significant greater ridge density than men.
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