Explain how the gonads develop before birth.

The development of gonads, which are the primary reproductive organs, begins during early embryonic development. In the early stages of development, the gonads are initially undifferentiated and can develop into either testes or ovaries depending on the genetic sex of the individual.

In individuals with a Y chromosome, the presence of the SRY gene on the Y chromosome triggers the development of testes. The SRY gene codes for a protein called testis-determining factor (TDF), which initiates the differentiation of the gonads into testes. The testes then begin to produce hormones such as testosterone and anti-Müllerian hormone (AMH), which are responsible for the development of male reproductive structures and the regression of female reproductive structures.

In the absence of the Y chromosome and the SRY gene, the gonads develop into ovaries. Without the influence of TDF, the gonads develop into ovarian follicles, which contain eggs and produce hormones such as estrogen and progesterone that are necessary for the development of female reproductive structures.

The development of the gonads is a complex process that is tightly regulated by genetic and hormonal factors. Any disruptions or abnormalities in this process can lead to disorders of sexual development, where individuals may have atypical reproductive anatomy or hormone levels.