It appears, then, that Sry may function indirectly to create testes by inducing mesonephric cell migration into the gonad. The existence of these two independent systems of masculinization is demonstrated by people having androgen insensitivity syndrome.
Wnt4: a potential ovary-determining gene on an autosome The WNT4 gene is another gene that may be critical in ovary determination.
Nat Genet — An equal number of males and females is, however, not always favored, even among autosomal genes e. For example, if an allele of an autosomal gene is beneficial to males but harmful to females and becomes linked to a dominant masculinizing mutation, then chromosomes that carry both the male-beneficial and male-dominant alleles create a novel Y that can replace the ancestral mechanisms.
Pannell JR The evolution and maintenance of androdioecy. Further extensions of the MAT region, possibly involving additional sex-antagonistic genes, led to the U and V chromosomes characterizing male and female gametophytes, as found, e. The loss of the paternal genome in sons benefits mothers but not fathers because these uniparental sons transmit more of a mother's genome to grandchildren mechanism of sex determination pdf in McAllen do biparental sons .
However, as we explain below, evidence from a broad array of organisms indicates that the link between sex chromosome heteromorphism and age is often far from direct. Steinemann S, Steinemann M Y chromosomes: born to be destroyed.
While blood concentrations of estrogen mechanism of sex determination pdf in McAllen higher in females than in males, the concentration of estrogen in the rete testis is even higher than that in female blood. B The external genitalia more Generally in this method, the sex is determined by amount of genes expressed across the two chromosomes.
Sox9: autosomal sex reversal One of the autosomal genes involved in sex determination is SOX9which encodes a putative transcription factor that also contains an HMG box. In other cases, sex of a fetus is determined by environmental variables such as temperature. Testosterone- and dihydrotestosterone-dependent regions of the human male genital system.
Other unusual systems include those of the swordtail fish [ clarification needed ] ;  the Chironomus midges [ clarification needed ] [ citation needed ] ; the juvenile hermaphroditism of zebrafish , with an unknown trigger;  and the platyfish , which has W, X, and Y chromosomes. The ZW sex-determination system is found in birds, some reptiles, and some insects and other organisms.
Bibcode : Natur. In both XY and XX gonads, the sex cords remain connected to the surface epithelium. Journal of Evolutionary Biology. However, under the influence of estrogen, derived first from the ovary but then from the mother and placenta, these infants are born with a female genital tract Langman and Wilson