Concerns the determination of the gonads. In mammals, determination strictlychromosomal; not influenced by the environment. Most cases- female = XX; male=XY Every individual organism has atleast one X Chromosome. Since the female has2 X chromosomes, each of her eggs posses one X chromosome. The male posses an Xand a Y, so therefore the male can produce 2 kinds of sperm, one with an Xchromosome 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 testisdetermining factor.
If a person had an innumerable number of x chromosomes andone y chromosome, they would be male. If a person is born with only a single xchromosome and no second x or y, then they develop as a female, but areinfertile.(not able to maintain ovarian follicles) More Primary SexDetermination- In the is absence of the Y chromosome , the primordial gonad bodydevelops into ovaries. the ovary then produces the estrogenic hormones, whichcontains estrogen and other such hormones, enabling the development of theMullerian duct into the uterus, fallopian tubes, and upper end of the vagina.
Inthe presence of Y chromosome, the testes form. The testes secrete two majorenzymes. The first hormone, AMH(anti-Mulllerian duct hormone), destroys toMullerian duct. The second, testosterone, stimulates the masculinization of thefetus. During this process the penis, scrotum, and other male anatomicalstructures form. The development of the primordial breast is inhibited. Thebody, therefore, has the female phenotype unless it is altered by two hormonescreated in the fetal testes.
The development of gonads is the only fetal organdevelopment process that has the chance of developing into more than one organ(under normal circumstances and barring mutations). The primordial gonad candevelop into either an ovary or a testis. Before the gonad develops into thetestes or ovary, it first goes through an indifferent stage, also known as abipotential stage, during which time it has neither male or femalecharacteristics. In humans, the primordial gonad first develops in the 4th weekand 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 theY chromosome. Individuals born with the short arm of the Y chromosome, but notthe long are males. Those born with the long end but not the short are actuallyfemale.
Through scientific research on XX males and XY females, the position ofthe testis-determining gene has been narrowed down to a small region. On theshort arm of the Y chromosome there is believed to be an area called the HMGbox, which stands for high-mobility group box. This HMG box is believed tocontain the genetic information to establish masculinity. There are two knownmajor genes in this HMG box that are believed to have an effect on thedetermining of sex, SRY and SOX9.
SRY (sex-determining region of the Y) is foundin XY males, is absent from XX females, is found in the rare XX males, and isabsent in the XY females. Many XY women were found to have a point mutation inthe SRY gene, which would prevent the SRY protein from binding to the DNA. Sincehumans are difficult to study, Scientists found a different way to study thisgene.
In mice, there is a gene homologous to SRY, which is named Sry. the mousegene also correlates with the presence of testes; it is present in XX males andabsent in XY females. To further test this theory of Sry being the testesdetermining gene, scientists injected the Sry sequence into XX fertilized micezygotes. In most instances the mice developed testes and the rest of the maleaccessory organs, but werent fertile(the presence of two X chromosomesprevents sperm formation in both mice and men). This is the majority of theevidence supporting this gene as the one that determines whether you are male orfemale. The function of SOX9 is unclear.
If a male is born without a functionalcopy of SOX9, then a syndrome called campomelic dysplasia develops. It involvesnumerous skeletal and organ systems. If born without SOX9, the male child diessoon there after from distress arising from defective bronchia and tracheas.However, 3/4 of those males born without SOX9 phenotypicaly appear to be femalesor hermaphrodites.
Since SOX9 is on the Y Chromosome, almost all women