5α-reductase is an enzyme that converts testosterone into dihydrotestosterone (DHT), the androgen responsible for masculinization of external genitalia. DHT also forms the scrotum and penis. Without this conversion, only partial masculinization is possible, and with no androgens, the female labia and clitoris are developed.

Conversion of Testosterone

Testes develop testosterone to help promote the wolffian system and the regression of the müllerian system with AMH (anti-müllerian hormone). The genital tubercle forms the penis and there is the development of the wolffian system (epididymis, vas deferens, and seminal vesicles). 

Rutgers University

The indifferent gonads at this point have been developed into either the ovaries or testes. The testes produce hormones that develops more masculine features, and the lack of these hormones allow the body to develop more feminine. The main difference is which duct system develops, which connects the gonads to the outer body wall. As one system begins development, the other degenerates.

Gonadal Hormones

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Sexual Differentiation Chart

Testes' Hormones

The lack of hormones created by the testes allows the body to develop more feminine. The genital tubercle forms the clitoris and there is the development of the müllerian system (oviducts, uterus, and inner vagina).

Learn Before

Related

Learn After