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ke_marshall t1_jabe17i wrote

Reply to comment by amador9 in Why does temperature determine the sex of certain egg laying animals like crocodiles? by insink2300

It depends on the species. Some have them, some don't: https://journals.plos.org/plosbiology/article/figures?id=10.1371/journal.pbio.1001899

My favorite fun fact is that sex determination in birds is exactly opposite to mammals: the females are heterogametic. They are ZW, while males are ZZ.

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MrinkysAnimalSide t1_jabfxzb wrote

It’s a great question and you’re exactly right! There are even some cases of fish having multiple sex chromosome systems interacting together to be XYZ. Cichlid fish in particular, well known for rapid speciation, show incredible evolution of sex chromosomes. In which case, you’re unlikely to find a single degenerate Y chromosome like you find in mammals.

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platoprime t1_jablhlw wrote

Why don't they use XY? Is it just alphanumeric numbering starting with the A chromosome? How do they pick the order of the chromosomes?

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lqstuart t1_jabmph1 wrote

https://en.wikipedia.org/wiki/X_chromosome

Tldr - they noticed the X chromosome was weird, so they called it X. Then Y was the next letter. Then Z and W came about to distinguish between the ZW system and the XY system (also it's important to note that the X chromosome is the X chromosome, period, whether it's in a mouse or a human or whatever--it refers to a specific thing that plays a specific role).

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Delirivms t1_jacmxfa wrote

So the band 'ZZ top' derives its meaning from homosexual birds?

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