Gonadal dysgenesis If a single or combination of these genes are mutated or deleted, downstream signalling is disrupted, leading to malformation of male external genitalia. SRY acts on gene SOX9 which drives Sertoli cell formation and testis differentiation. An absence in SRY causes SOX9 to not be expressed at the appropriate time or concentration, leading to a deficiency in testosterone and Anti-Müllerian hormone production. Inadequate levels of testosterone and Anti-Müllerian hormone disrupts the development of Wolffian ducts and internal genitalia that are key to male reproductive tract development. The lack of the male associated steroid hormones drives Müllerian duct development and perusal
Sexual selection in mammals Sexual selection in mammals Sexual selection in mammals started with Charles Darwin's observations concerning sexual selection, including sexual selection in humans, and in other mammals, consisting of male-male competition and mate choice that mold the development of future phenotypes in a population for a given species. A good example of intrasexual selection, in which males fight for dominance over a harem of females, is the elephant seal – large, oceangoing mammals of the genus "Mirounga". There are two species: the northern ("M. angustirostris") and southern elephant seal ("M. leonina") – the largest carnivore living today. Both species show extreme sexual