Testis determining factor

Testis-determining factor is a general term for the gene (or product thereof) that results in maleness in humans and some other species.

Current thinking is that certain genes will cause the chemical reactions that result in the development of testes. Embryos are gonadally identical, regardless of genetic sex, until a certain point in development; then the testis-determining factor causes male sex organs to develop, while lack of this factor will cause the embryo to develop as physically female.