Genetics of sexual development.

In humans, the choice between male or female development is genetically determined. Sex determination occurs as the undifferentiated and bipotential embryonic gonad becomes either testes or ovary. This process is influenced by the action of genes that have been discovered by genetics studies of sex-reversed patients, XY females, XX males, and XX true hermaphrodites. The development of the gonad is better known in males than in females. SRY, a gene located on the Y chromosome, triggers a complex genetic cascade leading to testicular development. Other genes such as DAX1, located on the X chromosome, antagonize the action of SRY and may influence ovarian development. Only a minority of sex-reversed patients can be explained genetically, suggesting that many genes influencing sex determination are yet to be discovered.