The female and male reproductive tracts originate from the same embryonic/fetal tissue. The gonads and internal and external genitalia begin as bipotential tissues. The indifferent gonad consists of a medulla and cortex. Human female and male embryos develop in the same way for the first 6 weeks, regardless of genetic sex (46,XX or 46,XY karyotype) (Figure 1.1). The one way to tell the difference between 46,XX and 46,XY embryos during this time period is by looking for a Barr body (“inactive” one X chromosome) or a Y chromosome. The medulla of the XY embryo will develop into the testes and the cortex will regress. In the XX embryo, the ovary will originate from the cortex and the medulla will decline. A complete 46,XX chromosomal complement is necessary for normal ovarian development. The second X chromosome contains elements essential for ovarian development.