The determination of a baby’s sex begins at the chromosomal level with the insemination of the ovum. Further sexual differentiation follows during the subsequent embryogenesis. However, chromosomal anomalies, gene mutations, and other exogenous or endogenous factors can cause disorders of sexual differentiation. These disorders manifest during childhood or at the latest in puberty, making patie...

Differentiation of mouse embryonic germ cells as male or female is dependent on the somatic environment of the gonad rather than the sex chromosome constitution of the germ cell. However, little is known about the initiation of germ cell sexual differentiation. Here, we traced the initiation of germ cell sexual differentiation in XX gonads using the Stra8 gene, which we demonstrate is an early ...

Sexual behavior in many mammals is characterized by its dependence on circulating titer of sex hormones and sexual dimorphism. Sexual dimorphism in female and male behavior depends, not on genetic sex but on early actions of sex hormone at a specific period during ontogenesis in each species. The period, termed the critical period for the brain sex differentiation, spans over gestational day 18...

The determination of a baby’s sex begins at the chromosomal level with the insemination of the ovum. Further sexual differentiation follows during the subsequent embryogenesis. However, chromosomal anomalies, gene mutations, and other exogenous or endogenous factors can cause disorders of sexual differentiation. These disorders manifest during childhood or at the latest in puberty, making patie...

The dogma that male and female embryos develop in identical fashion until SRY initiates Sertoli cell differentiation in the hitherto bipotential gonad is in need of reevaluation in the light of data that do not fit into this scheme. One of the exceptions that proves the rule of sex determination is true hermaphroditism, the existence of individuals with both testicular and ovarian tissue. Furth...

Southern swordtail fishes, which belong to the viviparous teleosts called Xiphophorus, are unique models for studies of evolution sex chromosomes. Monofactorial sex-determining systems, with either male or female being heterogametic sex, as well determination involving more than two chromosomes, found in swordtails and related species. Some species seem have originated by crossing between close...

There has recently been a revolution in our understanding of how the Drosophila sex-determination hierarchy generates somatic sexual dimorphism. Most significantly, the sex hierarchy has been shown to modulate the activities of well-known signaling molecules (FGF, Wnt and TGF beta proteins) and transcription factors (BAB and DAC) to direct various sex-specific aspects of growth and differentiat...