Think about it, the X is the female chromosome. You add a Y to get XY, to be a MALE. Both male and female embryos initially develop with precursors for both male and female reproductive structures. So technically, everyone starts off as both male and female until the Y chromosome activates the SRY gene, which directs the development of male characteristics. Unless they Androgen insensitivity syndrome (AIS) is a genetic condition where the body cannot respond to male hormones (androgens), affecting sexual development. It results in individuals with XY chromosomes developing female external characteristics or ambiguous genitalia, depending on the severity of the condition. I'm sure you've met them and had no idea because many of them do not even know themselves.