Medical visualization comparing the development of male and female urogenital organs during the 8th week. At left is the developing Mullerian duct and ovary of the female; at right is the developing Wolffian duct and testicle of the male. At 5 weeks of development, all fetuses have two undifferentiated sets of ducts: the Mullerian ducts and the Wolffian ducts. After 5 weeks, differentiation begins as the sex-determining region Y (SRY) gene on the Y chromosome signals testicle development in the male fetus. As the testicles form, they start producing anti-Mullerian hormone (AMH) and testosterone. As a result, the Mullerian ducts degenerate and the Wolffian ducts are stimulated to grow into the epididymis, vasa deferentia, and seminal vesicles. Since the female fetus lacks SRY, and consequently, AMH and testosterone, ovaries will form instead of testicles, and the Mullerian ducts will grow into the uterus, fallopian tubes, and cervix, and the Wolffian ducts will degenerate.

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