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发表于 2006-5-18 18:01
Whether men will extinct in the future is a question.
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Men Aren't Going Extinct
NEW YORK - Good news for men: The male sex chromosome isn't going extinct anytime soon. Researchers have found, contrary to the popular notion, that the male Y chromosome is not gradually decaying away.
In recent years, researchers have theorized that the male sex chromosome is heading for extinction over the next few million years. Unlike other chromosomes, the Y chromosome has no partner with which to swap genes when one gets damaged. The Y contains a wimpy 27 genes (versus 1,000 or so for the X chromosome), and has shed the vast majority of its genes since it diverged from ancestor chromosomes roughly 300 million years ago. It has been likened to a genetic wasteland.
But now researchers at the MIT-affiliated Whitehead Institute have compared the human Y chromosome to the chimpanzee counterpart, searching for genes that men may have lost or degraded since humankind diverged from chimps six million years ago. To their relief, they found not a single gene has been lost in that long period, indicating that the Y isn't falling after all.
By contrast, the researchers found that the chimpanzee male chromosome has lost five genes over the last six million years, which may be due to chimps' promiscuous sexual habits, the researchers theorized. Men have one X and one Y chromosome, while women have two X chromosomes.
"Somehow this idea...that the Y chromosome is headed for extinction...has achieved tremendous market penetration," says Whitehead geneticist David Page, the senior author of the study. "But despite all the doomsday scenarios, it actually looks like the Y is sailing along quite nicely. It has established a new lifestyle with fewer genes. Our species has a long to-do list, but I think we can cross this problem off the list. You can sleep a little better now."
The sex chromosome work is being published this week in the British journal Nature as part of a package of articles on the sequencing of the chimpanzee genome.
In several other articles, researchers from the University of Washington and elsewhere searched for key genetic differences that could help explain what makes us human. Overall, the researchers found that human and chimps were 98.8% genetically identical, with a mere 35 million chemical letters that differ between the chimp and human books of life. By another measure, searching through larger sections of DNA for whole sentences that are copied or deleted, the researchers found a slightly larger 2.7% variation between the two species.
"The chimp data allows us to provide a comprehensive catalog of all the variations between chimp and human," says University of Washington geneticist Evan Eichler. This data will help to narrow down to the minority of changes crucial to our human-ness.
Still, after all this work, researchers are only at the very earliest stages of figuring out why we are so much smarter than monkeys.
"The original idea was by comparing [chimps' genes]with the human genome we would discover why we write poetry or become reporters. Sadly today we can say almost nothing about that topic that we couldn't say before the chimp genome was done," says Whitehead Institute's Page. "We genomicists can pile up the DNA letters very quickly but are very primitive readers of the text. It is an overstatement to say we can read it at the first grade level."
The chimpanzee genome data provides another possible tool for companies mining gene data for key disease causing genes and genetic variations, although the mouse genome and other model systems such as tiny roundworms are likely to remain mainstays for this sort of work.
Companies known for their gene work include Celera Genomics Group and Human Genome Sciences (nasdaq: HGSI - news - people ). Big drug companies, including Merck (nyse: MRK - news - people ) and Pfizer (nyse: PFE - news - people ) and GlaxoSmithKline (nyse: GSK - news - people ) have also invested heavily in newfangled gene research over the years.
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