Explain in an easy way and function

BETWEEN Reproductive development & sex determination XY The germ cells 'set up shop' in what will become the future ovary or testes = here's where chromosomal sex matters significantly!!! In XY males: the protein encoded by the SRY gene \"Sex determining Region on Y chromosome\" signals to cells around the germ cells to begin producing the steroid hormone testosterone - Testosterone tells the male gonad to develop into a testicle (it also tells cells elsewhere in the body to begin growing a penis and a male brain). In XX females: it's the lack of the Y that matters... more estrogen, lower testosterone leads to female development by default: ovaries, uterus, vagina... How do we know??? Androgen Insensitivity Syndrome: XY individuals with a mutated, non-functional testosterone receptor are externally female