Describe the development of reproductive organs in a fetus of each gender. Which genes, gene products, and hormones are involved in the sex differences? Which sex-related hormones are circulating in high concentrations in a pregnant woman compared to a nonpregnant woman? Do these hormones cross the placenta (if you are uncertain, consider hormone chemical class relative to membrane permeability to make an educated guess)? Assuming these hormones do cross the placenta, how do they affect the hormonal environment inside the fetus, and how does this relate to fetal reproductive development?

Question

What will be an ideal response?

Answer 1

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-Müllerian 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.