Sex chromosomes come in pairs, such men have X-Y and women have X-X. Around 320 million years ago when the first Y male determining chromosome appeared, both the X and Y chromosomes had roughly the same number of genes, actually sharing 800 genes. In time, the Y chromosome has lost 1,393 of its 1,438 original genes over the course of its existence. With a rate of genetic loss of 4.6 genes per million years, the Y chromosome may potentially lose complete function within the next 10 million years, or so some scientists claim. Currently, the human Y carries a mere 19 of its ancestral genes shared with the X chromosome, out of a once 800 strong, bringing the total number of genes in the human Y to 27.
This would mean that in a few million years, the world would be dominated by women alone, leaving only artificial reproduction as an exclusive option – highly practical, not all that fun. Fear not, for Jennifer Hughes at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, along with colleagues, have found that the Y chromosome is here to stay.
The researchers sequenced the Y chromosome of the rhesus macaque, a very close relative of humans, from which it diverged paths some 25 million years ago. It was found that the monkey’s Y has 20 genes shared with its X, of which 19 are shared with the human Y. This suggests that the human Y chromosome has lost only one gene since humans and macaques last shared a common ancestor. The research, thus, provides direct evidence that the linear extrapolation model is flawed.
“We finally have empirical data that the Y chromosome has held steady over the last 25 million years,” says Hughes. “Most of the Y chromosome’s gene loss happened almost immediately after it stopped recombining with the X chromosome.” The 19 surviving genes probably have vital biological functions, she says, and so aren’t going anywhere anytime soon.
Here’s to men!
The research was published in the journal Nature. Image credit.