2. How does the internal sexual organs develop?

The human embryo contains two structures that contribute to the reproductive system – the Wolffian duct and the Mullerian duct. If the person has XY chromosomes, the SRY gene on the Y chromosome direct the gonads to develop into testis. The testes produce testosterone, which along with dihydrotestosterone promote the development of the Wolffian duct into the epididymis, vas deferens, seminal vesicles and the ejaculatory ducts, which are parts of the male reproductive system. In addition, they also produce the Mullerian inhibiting substance, which causes regression of the Mullerian system. If the person has XX chromosomes, the gonads develop into ovaries. The Mullerian system develops into the fallopian tubes, uterus and upper part of the vagina, which are parts of the female reproductive system, while the Wolffian duct regresses.