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Sex Determination in mammals

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Sex Determination in mammals Introduction Mammals are large animals with long life cycles. They produce relatively few gametes and so use sexual reproduction to increase variation in order to adapt to environmental conditions with the maximum efficiency. As organisms have become larger and taken the form of the mammals we see today, a greater specialisation within each sex becomes an advantage; one member usually concentrating on producing energy-expensive eggs whilst the others produce large quantities of sperm. This process cumulates in the mammalian system of viviparity, when the embryo develops inside the female and the male will usually provide them both with food. With this increasing investment in young the potential dangers of inbreeding increase and the greater the need for mechanisms to insure outbreeding. In this presentation we plan to highlight how the genes involved in the determination of the different sexes work to ensure that the highly conserved mechanisms for sexual reproduction are passed on to the progeny. ...read more.


SRY - Sex Reversal on Y gene In the genital ridge and in the developing gonads although expression decreases in female gonads with time. Responsible for reversing the default sex pathway (female) and activating the male pathway genes (MPG), leading to male development. WT1 - Wilm's Tumor-association gene In the genital ridge. Involved in early gonad and kidney development. SF1 - Steroidogenic Factor In the genital ridge. It is a nuclear receptor, part of the orphan receptors family. It acts as a gene regulatory protein. LIM1 - In the genital ridge. Involved in the early differentiation of the intermediate mesoderm and the urinogenital system as a whole and has a general role in early gonad development. AMH - Anti Mullerian Hormone In the sertoli cells, once differentiated. Responsible for recessing the mullerian ducts in the male pathway, which would otherwise become female genitalia. ...read more.


Responsible for degrading the Mullerian duct in males, which gives rise to the oviducts and uterus in the female. Testosterone In the leydig cells. Differentiation of the Wolffian duct. Oestrogen In the ovaries It helps with ovarian differentiation. A male (XY) with AMH and testosterone but without testosterone receptors cannot respond to testosterone but do respond to androgen made in their adrenal glands which gives them a female appearance, because they still respond to AMH the Mullerian duct degenerate and the result is a normal sterile women without a uterus and oviducts but with testes in their abdomen. This shows that the effects of the hormones are vital. Hormones in puberty... Hormones Where it is produced What it does Testosterone In the leydig cells in male gonads. Secondary sexual characteristics in the male, eg. Facial hair, deepening of voice. Oestrogen In the graafian follicle. Secondary sexual characteristics in the female, eg. Breasts and hip development Dihydrotestosterone In the leydig cells in the male gonads External genitalia, facial and body hair distribution, acne, temporal recession of hair line. ...read more.

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