It's a very interesting combination of factors here, and they're also making the observation that this could be how the original XX/XY split occurred. Sexual g

It's a very interesting combination of factors here, and they're also making the observation that this could be how the original XX/XY split occurred. Sexual genetics are actually a lot more complicated than people think. There are YY "supermale" people, though it's more common in fish which gender-flip depending on population balance leading to XY males breeding with XY females. A YY male will always produce male children. There's also XXY, XXXY and so on which is where things get even more complicated.