text: In the prenatal period, virilization refers to closure of the perineum, thinning and wrinkling (rugation) of the scrotum, growth of the penis, and closure of the urethral groove to the tip of the penis. In this context, masculinization is synonymous with virilization.
  Prenatal virilization of genetic females and undervirilization of genetic males are common causes of ambiguous genitalia and Disorders of sex development
  For many years, it was widely believed that in mammals, the female is the "default" developmental pathway, and the SRY gene on the Y chromosome is responsible for suppressing the development of female characteristics and stimulating males characteristics. In this scenario, an embryo would passively develop female sexual characteristics without intervention by the SRY gene. However, in the early 2000s, other genes, such as WNT4 and RSPO1, were discovered that perform the opposite function  – i.e., genes which suppress masculinization and stimulate feminization.
  Two processes: defeminization, and masculinization, are involved in producing male typical morphology and behavior.