Livre d'Or

It's true that having chromosomes other than XX or XY is pretty rare

Note, incidentally, that there are at least two intersex conditions where people have XY karyotypes, and yet they are born with female genitalia, look female, feel female, are treated as female by themselves, their families, society and the law - in short, they're female, and this has presumably been going on since the dawn of humanity or even before. Furthermore, the genetic mechanisms in these two conditions are completely different.