Sex Hereditary Determination Essays - Sex, Epigenetics,

Sex Hereditary Determination Concerns the determination of the gonads. In mammals, determination strictly chromosomal; not influenced by the environment. Most cases- female = XX; male= XY Every individual organism has atleast one X Chromosome. Since the female has 2 X chromosomes, each of her eggs posses one X chromosome. The male posses an X and a Y, so therefore the male can produce 2 kinds of sperm, one with an X chromosome and one with a Y chromosome. If an offspring receives an X and a Y, then it will be a male. TheY chromosome carries a gene that encodes a testis determining factor. If a person had an innumerable number of x chromosomes and one y chromosome, they would be male. If a person is born with only a single x chromosome and no second x or y, then they develop as a female, but are infertile.(not able to maintain ovarian follicles) More Primary Sex Determination- In the is absence of the Y chromosome , the primordial gonad body develops into ovaries. the ovary then produces the estrogenic hormones, which contains estrogen and other such hormones, enabling the development of the Mullerian duct into the uterus, fallopian tubes, and upper end of the vagina. In the presence of Y chromosome, the testes form. The testes secrete two major enzymes. The first hormone, AMH(anti-Mulllerian duct hormone), destroys to Mullerian duct. The second, testosterone, stimulates the masculinization of the fetus. During this process the penis, scrotum, and other male anatomical structures form. The development of the primordial breast is inhibited. The body, therefore, has the female phenotype unless it is altered by two hormones created in the fetal testes. The development of gonads is the only fetal organ development process that has the chance of developing into more than one organ (under normal circumstances and barring mutations). The primordial gonad can develop into either an ovary or a testis. Before the gonad develops into the testes or ovary, it first goes through an indifferent stage, also known as a bipotential stage, during which time it has neither male or female characteristics. In humans, the primordial gonad first develops in the 4th week and remains indifferent until the 7th week. Sex Determinant genes- In humans, the major genes for the testis determining factor reside on the short arm of the Y chromosome. Individuals born with the short arm of the Y chromosome, but not the long are males. Those born with the long end but not the short are actually female. Through scientific research on XX males and XY females, the position of the testis-determining gene has been narrowed down to a small region. On the short arm of the Y chromosome there is believed to be an area called the HMG box, which stands for high-mobility group box. This HMG box is believed to contain the genetic information to establish masculinity. There are two known major genes in this HMG box that are believed to have an effect on the determining of sex, SRY and SOX9. SRY (sex-determining region of the Y) is found in XY males, is absent from XX females, is found in the rare XX males, and is absent in the XY females. Many XY women were found to have a point mutation in the SRY gene, which would prevent the SRY protein from binding to the DNA. Since humans are difficult to study, Scientists found a different way to study this gene. In mice, there is a gene homologous to SRY, which is named Sry. the mouse gene also correlates with the presence of testes; it is present in XX males and absent in XY females. To further test this theory of Sry being the testes determining gene, scientists injected the Sry sequence into XX fertilized mice zygotes. In most instances the mice developed testes and the rest of the male accessory organs, but weren't fertile(the presence of two X chromosomes prevents sperm formation in both mice and men). This is the majority of the evidence supporting this gene as the one that determines whether you are male or female. The function of SOX9 is unclear. If a male is born without a functional copy of SOX9, then a syndrome called campomelic dysplasia develops. It involves numerous skeletal and organ systems. If born without SOX9, the male child dies soon there after from distress arising from defective bronchia and tracheas. However, 3/4 of those males born without SOX9 phenotypicaly appear to be females or hermaphrodites. Since SOX9 is on the Y Chromosome, almost all women