If FWers detect that I'm more than a little annoyed that a professor should write a book for widescale reading on something that, it turns out, is still scientifically controversial, then they would be right.
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It appeared I was wrong (in "065. The future will be in our genes") to take the work of Bryan Sykes, Professor of Human Genetics of Oxford University at face value. His statement about the deterioration of the male's Y-chromosome over the next 125,000 years, and due to be published next month in a Bantum book, is far from accepted by other researchers. The stability of the Y chromosome is still controversial and obviously needs a lot more research. Bryan Sykes wrote (in his Sunday Times extract):
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In June, the journal Nature announced the almost complete sequence of a human Y-chromosome, which revealed something completely unexpected. There were signs that amid the wreckage of once-active genes, the Y-chromosome is still capable of safe-guarding genes -- but only by effectively having sex with itself. Does this mean that men are now saved from extinction? Sadly not. Does the news extend men's day of reckoning? Unfortunately not.
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And a list member wrote to me immediately as follows:
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Why not? It sure sounds self-maintaining to me. Why didn't the Y chromosome among our pre-human ancestors become extinct millions of years ago? The author hasn't made his case. My "politicized pseudo-science" alarm-bell is going off right now.
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And this was followed up today by someone sending me the following report from the Australian BC which refers to research contradictory to Syke's case being published recently in the journal Nature:
<<<< MALE Y-CHROMOSOME HERE TO STAY
Bob Beale
The Y chromosome is no longer longer puny despite being so much smaller than the X chromosome. The human male sex chromosome does have the ability to repair itself and may
not be headed for extinction as had previously been thought, according to a surprising new study.
A 40-strong team of researchers led by Dr David Page of the Whitehead Institute at the Massachusetts Institute of Technology, report their findings in this week's issue of the journal Nature. As well as having a previously unknown and elaborate back-up system for self-repair, the Y chromosome also carries 78 genes, almost double the previously known tally, the reseachers report.
"The Y chromosome is a hall of mirrors," says Page, whose team has for the first time identified the full genetic sequence of a Y chromosome, from an anonymous donor. Earlier studies had suggested that the Y chromosome carried only a few dozen genes, compared with more than 1,000 known on the X chromosome. Both the male Y and female X-chromosomes are thought to have originally been the same size, but after the Y took on the sex-determining role for maleness it apparently began to lose genes. At this time it also lost the ability to pair up exactly with its partner and to swap faulty genes for good ones, as the other 22 pairs of non-sex chromosomes do.
A team of Australian researchers led by Dr Jenny Graves, of the Research School of Biological Sciences at the Australian National University in Canberra previously found that the Y chromosome had been losing five genes per million years. Dr Graves had thus predicted that the chromosome might be heading for extinction within five to 10 million years.
But Page says that the Y's full genome sequence has revealed that scientists generally had underestimated both its number of genes and its powers of self-preservation. Page's team believes the Y has developed an apparently unique way of pairing up with itself. They found that many of its 50 million DNA "letters" occur in sequences known as palindromes. Like their grammatical counterparts, these sequences of letters read the same forward as backward but are arranged in opposite directions -- like a mirror image -- on both strands of the DNA
double helix. This means that a back-up copy of each of the genes they contain occurs at each end of the sequence.
When the DNA divides during reproduction, the team believes, it opens an opportunity for genes to be shuffled or swapped and faulty copies to be deleted. But this deletion process may not have had entirely positive consequences because a proportion of cases of male infertility have been found to be the result of deletions of key genes in the Y chromosome. The team found, for example, that the 27 genes the Y still shares with the X often do not
function on the Y, which means that it is still degrading.
Page predicts, however, that the new understanding of the Y's structure and vulnerability to decay will help to improve infertility testing for men. "We have a greater knowledge of where the Y tends to break," says Page. Testing needs to be updated to reflect our better understanding from the finished sequence."
Friday, 20 June 2003 Bob Beale - ABC Science Online http//www.abc.net.au/science/news/stories/s884493.htm >>>>
Keith Hudson, 6 Upper Camden Place, Bath, England
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