I've forgotten which is the X and which is the Y - but - this much I DO remember. Males are either XX or YY (only because I don't remember which is which), and women are both, X and Y, XY. Or vice versa, males are YY and women are still XY. Women can pass on EITHER the X or the Y. Males can ONLY pass on the one 'cause that is all they've got and what makes them male.