Men are NOT dying out: DNA analysis reveals the Y chromosome is here to stay - and it plays more of a role than first thought

Previous research claimed men could be extinct in five million years

This is because the male chromosome Y has a small range of unique genes

It's also lost 90% of genes it used to share with the female X chromosome

Other chromosomes, by comparison, have thousands of unique genes

By comparing the human Y sequence with a chimpanzee's, researchers found it lost just one ancestral gene in the past 25 million years

They also found it plays a role in determining health differences between the sexes



Some experts claim the male Y chromosome (pink) is on the way out. Yet DNA analysis has found a small set of unique genes have remained for 200 million years

Not only is the male chromosome here to stay - following exaggerated reports of its demise - it also plays a much wider role than first thought.



Researchers from Massachusetts have discovered that despite its decay, the Y chromosome has preserved a small set of genes over millions of years that have ensured the survival of men.

And most have little, if any, role in sex determination or sperm production, according to the study.



Instead, they have been discovered to play a vital role in determining the differences between the sexes in terms of health and disease.

The findings, published in the journal Nature, suggest these Y-linked genes could be contributing to differences in how susceptible the different sexes are to disease, and how severely it affects them.



Professor David Page, of the Whitehead Institute for Biomedical Research in Massachusetts, said: ‘This paper tells us not only is the Y chromosome here to stay but we need to take it seriously - and not just in the reproductive tract.

‘There are approximately a dozen genes conserved on the Y, expressed in cells and tissue types throughout the body.

‘These are genes involved in decoding and interpreting the entirety of the genome. How pervasive their effects are is a question we throw open to the field - and it's one we can no longer ignore.’

He said his research will allow his lab to change from proving the so-called 'rotting Y theorists' wrong.



Using DNA analysis, stock image pictured, researchers discovered that most of the remaining genes have little, if any, role in sex determination or sperm production. Instead, they have been discovered to play a vital role in determining the differences between the sexes in terms of health and disease

HISTORY OF THE Y CHROMOSOME Prior to 200 million years ago, when mammals were still relatively new on Earth, early versions of the X and Y sex chromosomes existed as interactive pairs.

With each generation, they swapped a few genes so that offspring were a genetic mix of their parents.

Then the gene for male features became fixed on the Y chromosome, and attracted other male-specific genes such as those controlling development of the testes, sperm and semen. Many of these turned out to be harmful for females, so the X and Y stopped swapping genes and started to evolve separately. Today women have a matched pair of X chromosomes while men have an XY pair. Because the X and Y cannot swap genes it is more difficult for mistakes in the Y chromosome to be corrected. This has made it more sensitive to natural selection, and led to its degradation over time, scientists believe.



The belief was based on claims the chromosome's 1,400 genes had fallen in number to just 45 in the last 300 million years and this would carry on until it disappeared - making men extinct.

Over the past decade Professor Page and colleagues have been debunking this argument.

The loss of content on the Y is not in dispute, and Professor Page's own lab has found the chromosome retains only 19 of over 600 genes it once shared with its partner - the female X chromosome.

But by comparing the sequence of the human Y with that of the chimpanzee and the rhesus macaque, the researchers discovered the chromosome has lost only one ancestral gene over the past 25 million years.



The latest study maps the evolution of the Y chromosomes of five more distantly-related mammals - the marmoset, mouse, rat, bull and opossum.

This revealed a set of broadly expressed genes across all eight species - and such stability and conservation is no accident with each having a counterpart on the X.

Professor Page explained: ‘This is not just a random sampling of the Y's ancestral repertoire. This is an elite bunch of genes.’

Lab researcher Dr Winston Bellott added evolution is telling us these genes are really important for survival because they've been selected and purified over time.

The next step will be to determine what this set of Y genes is actually doing, which is not yet clear.



Cells in females which have two X chromosomes, and are referred to as XX, are subtly but fundamentally different from male XYs.

By comparing the sequence of the human Y chromosome with that of the chimpanzee, stock image pictured, and the rhesus macaque, the researchers discovered the chromosome has lost only one ancestral gene over the past 25 million years

And they vary throughout the body in tissues and organs that show no obvious anatomic differentiation.

Dr Bellott said: ‘They're similar, but biologically different.



‘Yet we have cell biologists and biochemists actively studying cells without any idea whether the cells are XX or XY.



This is so fundamental to biology and biomedicine - and yet no one's really paid much attention to it.’

The researchers said what's needed is a biochemical catalogue of the differences between XX and XY cells - including variability in such processes as gene expression and protein production.

Professor Page said this pursuit could have enormous implications for human health.