Describe the development of reproductive organs in a fetus of each gender

Each fetus initially has the same bipotential structures. These become distinct testes or ovaries and the internal and external genitals typical of each sex by 10 weeks. In males, the change in bipotential structures begins with expression of the SRY gene on the Y chromosome, which secretes testis-determining factor. Once the testes develop, they secrete androgens and anti-Mullerian hormone, which completes the masculinization of the fetus. The female structures develop in the absence of SRY and consequent hormones. Maternal estrogen and progesterone are very high, and as steroids they easily cross the placenta, creating a very female hormonal environment in a fetus of either gender. This underscores the importance of the male hormones in masculinizing male fetuses.