Reproductive

Without a Y chromosome (and its SRY gene), the indifferent gonad develops into an ovary and the default phenotype is female. SRY drives testis development.

SRY induces testis development: Sertoli cells secrete Müllerian inhibitory factor (MIF/AMH) and Leydig cells secrete testosterone.

Fallopian tubes, uterus, cervix, and the upper one-third of the vagina.

Driven by testosterone, the Wolffian ducts form the seminal vesicles, epididymis, ejaculatory duct, and ductus deferens (SEED).

DHT (converted from testosterone by 5α-reductase) drives development of the prostate, penis, scrotum, and male external genitalia.

Ambiguous or female-appearing external genitalia at birth (low DHT) with normal internal male structures; virilization (and growth of external genitalia) occurs at puberty when testosterone surges ('penis at 12').