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Men might escape extinction according to monkey Y chromosome study

27 February 2012

By Ruth Saunders

Appeared in BioNews 646

Men may not be on the brink of extinction after all, according to a study on the evolution of the human Y chromosome.

Previous research has suggested that the Y sex chromosome, carried only by men, is decaying genetically at such a rate that men would become extinct in five million years' time.

However the study, carried out by Dr Jennifer Hughes and her team at the Whitehead Institute for Biomedical Research in Massachusetts in the US, suggests that the Y chromosome may not vanish after all.

The study, published in Nature, compared the human Y chromosome to that of the rhesus monkey which is separated from humans by 25 million years of evolution. The monkey Y chromosome hasn't lost a single ancestral gene in the past 25 million years, whereas the human Y has lost just one of these ancient genes in the same period.

In a previous Nature paper, Dr Hughes and her team also compared the human Y chromosome with that of the chimpanzee, which is separated from humans by 6 million years of evolution.

Both comparative studies found that genetic decay of the human Y chromosome has been minimal, losing no further genes in the past 6 million years and only one in the past 25 million years.

'This paper simply destroys the idea of the disappearing Y chromosome', said Dr Hughes. 'Now our empirical data fly in the face of the other theories out there. With no loss of genes on the rhesus Y and one gene lost on the human Y, it's clear the Y isn't going anywhere'.

Professor Mark Pagel, Professor of Evolutionary Biology at the University of Reading, UK, told BBC News: 'It's a very nice piece of work, showing that gene loss in the male-specific region of the Y chromosome proceeds rapidly at first - exponentially in fact - but then reaches a point at which [...] this process [is brought] to a halt'.

Around 300 million years ago, the X and Y chromosomes were the same size. Today, however, the Y chromosome has less than 30 genes and the X has over 800.

Genetic decay of the Y chromosome has occurred because, unlike the two X chromosomes in women, there is little crossing over of genetic material between the Y and the X chromosome during reproduction.

'The X is fine because in females it gets to recombine with the other X but the Y never gets to recombine over almost its entire length, and shutting down that recombination has left the Y vulnerable to all these degenerative forces', Dr Hughes told BBC News, 'which is why we're left with the Y we have today'.

The findings have not been universally accepted. Talking to the Guardian, Professor Darren Griffin of the University of Kent, UK, maintained: 'If you draw a straight line, the Y chromosome's demise would come four or five million years from now'.

He added: 'Everyone agrees that the demise of the Y chromosome, if it happens, does not mean the demise of the human male. All that will happen is that the process of sex chromosome evolution will start again'.

 

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