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End of men? Not just yet, say scientists investigating mysteries of male Y chromosome

  • @SteveAConnor

Reports of the demise of the male Y chromosome have been greatly exaggerated according to scientists who believe that the “end of men” is a gender apocalypse too far.

Two independent studies of the diminutive Y chromosome, which is inherited solely down the male line, have failed to find evidence to support the widely held theory that its evolutionary days – and those of its owner – are numbered.

A detailed genetic analysis of the Y chromosomes of a wide range of mammalian species, including humans, shows that far from continuing to wither away unremittingly, it has remained remarkably stable for at least the past 25 million years.

The research also found that the few remaining genes on the Y chromosome include some that perform vital regulatory control of other genes that are active throughout a man’s body – making each of his cells distinctly and subtly different from those of a woman.

This would suggest that medical treatments should in future be tailored more towards a patient’s gender, and that doctors may have more reason to treat men and women differently according to their sex, said Professor David Page, director of the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts.

“There is a clear need to move beyond a unisex model of biomedical research, which means we need to move beyond a unisex model of our understanding and treatment of disease,” said Professor Page, who led one of the research teams.

Henrik Kaessmann of the University of Lausanne, who led the other team, said that the findings explode the myth that the Y chromosome is primarily about the genes involved in male reproduction.

“Now it is clear that the Y chromosome is not specific to males so to speak but also important for functions throughout the body,” Professor Kaessmann said.

Men inherit both a Y and an X chromosome, and women have two X chromosomes. However, scientists believe the Y chromosome is a withered remnant of the X chromosome from which it originally evolved.

Hundreds of millions of years ago, genetic decay ravaged the Y chromosome, leaving it with just three per cent of its ancestral genes, compared with 98 per cent on the corresponding X chromosome of women.

This rapid loss of genetic function was widely seen as a portent of a premature demise for the Y chromosome, and of the male sex in general. The Oxford geneticist Professor Bryan Sykes, for instance, estimated in 2003 that men have about 125,000 years left before they become extinct.

However, the latest studies, published side by side in the journal Nature, demonstrate that although the Y chromosome has retained only 19 of the 600 genes it once shared with the X chromosome, it has lost only one of its genes in the past 25 million years, and those that have remained continue to serve vital functions throughout the male body – and not just in his reproductive organs.

“This [study]  tells us that not only is the Y chromosome here to stay, but that we need to take it seriously, and not just in the reproductive tract,” Professor Page said.

“There are approximately a dozen genes conserved on the Y that are expressed in cells and tissue types throughout the body. These are genes involved in decoding and interpreting the entirety of the genome…this is an elite bunch of genes,” he said.

Daniel Bellott, a research scientist at the Whitehead Institute, said that the few genes left on the Y chromosome must be incredibly important for male survival and show just how streamlined the Y chromosome has become.

“Evolution is telling us these genes are really important for survival. They’ve been selected and purified over time,” Dr Bellott said.

“We think that the Y chromosome is holding on to these last few genes to ensure male viability. The Y is sort of streamlined. It’s a minimal second sex chromosome,” he said.