Why is the sex chromosomes of humans and most animals written as XY while for birds it is ZW
In: Biology
Sorry for my funny first thought: I immediately thought it’s because a duck’s dong is shaped like a cork and he’s gotta wind that up the bottom of the W.
How on earth did this split come about. The [article](https://gizmodo.com/why-do-birds-have-zw-sex-chromosomes-instead-of-xy-1682328912) linked below says
Your sex characteristics were determined by X and Y chromosomes, same as most other creatures from humans to fruit flies. So why do birds and butterflies have ZW chromosomes instead?
WTF? How do birds and butterflies share a chromosome, but humans and fruit flies have another!? That would imply that butterflies and birds are more closely related that fruit flies and butterflies. And humans are closer to fruit flies than birds.
Can someone explain?
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