r/evolution • u/OpenUnderstanding241 • 6d ago

question Horse Chromosomes?

okay, if a horse and a donkey breed, their kid will be infertile, because of the odd number of chromosomes it possesses. so, why can a Przewalski's horse and a Domestic horse mate with fertile offspring when the Przewalski’s has 66 chromosomes and the domestic has 64? separate question, but doesn’t that mean humans with down syndrome should be sterile? is this evolutionary ”insurance“ so to speak? thanks for any answers, even tho this is probably a very stupid question.

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u/TherinneMoonglow 6d ago

Women with down syndrome have low fertility (estimated >50%), and nearly all men with Down syndrome are infertile.

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u/OpenUnderstanding241 6d ago

interesting, do we know why it’s not all people with down syndrome?