X-Y Evolution

Diagram of X and Y chromosome evolution

The X and Y chromosomes are derived from an ordinary pair of chromosomes and began diverging from each other about 300 million years ago. Since that time, the X chromosome has lost few if any genes. The Y chromosome, on the other hand, has lost all but a handful of its unpartnered genes. Over the past 6 million years of evolution, since the human and chimpanzee ancestors parted ways, the human Y chromosome has suffered no further gene loss, while 5 of the chimpanzee genes have become severely damaged.

Y Gene Loss

Diagram of Y gene loss

Since the time of the divergence of the X and Y chromosome roughly 300 million years ago, the Y chromosome has lost nearly all of its unpartnered genes. This has led some to predict that, given a constant rate of decay, the Y chromosome will be completely devoid of functional genes in 10 million years. The chimpanzee ancestors diverged from ours about 6 million years ago. By comparing the gene catalog of the chimpanzee Y chromosome to ours, it is clear that the human Y chromosome has not lost any of its unpartnered genes in the past 6 million years.


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Human Y chromosome stays intact while chimp Y loses genes

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