Repeated evolution: Sex chromosomes evolved independently, many times, in various species

Sex chromosomes evolved not once, but many times, independently … stuff happens …

Sex chromosomes are derived from autosomes and have evolved independently many times in different lineages. For example, the human X and Y chromosomes originated about 200-300 million years ago in eutherian mammals after the split of monotremes,

and sex chromosomes evolved independently in birds, snakes, and multiple times in other reptiles, amphibians and fish; they also formed repeatedly in many invertebrate taxa and plants

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