Why is the sex chromosomes of humans and most animals written as XY while for birds it is ZW

Question

Why is the sex chromosomes of humans and most animals written as XY while for birds it is ZW

In: Biology

Answer 1

Although XY and ZW control sex determination, they are otherwise complete dissimilar. There are zero genes conserved between humans and birds in these chromosomes, and they even function differently. For example, in humans a mismatched pair (XY) is male while it birds (ZW) it’s female. A ZZ bird is male. Here’s a good non-technical article about it.

https://gizmodo.com/why-do-birds-have-zw-sex-chromosomes-instead-of-xy-1682328912