Role of Hormones: In the eighth week of gestation or pregnancy, the hormone testosterone is produced by testes. Some part of this hormone gets converted into closely related substance dihydrotestosterone, or DHT. The male hormones are known as androgens. The DHT stimulates the growth of all purpose embryonic structures like glans penis, penis shaft and scrotum, which otherwise develop into the female embryonic structures like the clitoris, labia minora and labia majora.
Embryos start constructing with two sets of ducts, known as the Mullerian ducts and the Wolffian duct. If the testes is not present, then the Wolffian ducts degenerate and Mullerian ducts grow into uterus, fallopian tubes, and the inner part of the vagina. In the presence of testes, the androgens promote the Wolffian duct to grow into seminal vesicles, vas deferens and epididymis. While at the same time, a testicular protein called Mullerian inhibiting factor prevents the Mullerian ducts from developing into the internal female organs. In this way, the genetic information on sex chromosomes is responsible for the primary sex determination events, hence the sex is determined at the time of fertilization.
After the development of gonads under normal conditions the sex hormones help in the development of secondary sexual characteristics, which include growth of beard, change of voice in males and breast development in females. Thus the phenotypic differences between males and females are regulated by hormones, which are produced on the basis of genetic information programmed in the genome.