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Y Guy Defends his Chromosome Against Charges of Rot

BOSTON, Oct. 4 - It may be a man's world, but the Y chromosome, that potent master code for the male mammal, gets no respect from contemporary geneticists. With its bizarre habit of shunning genetic crossovers, it has earned a reputation as a rotting "junk heap" of DNA that is hurtling toward evolutionary obsolescence, Whitehead Institute researcher David Page said at his talk during Friday morning's plenary session at the Genome Sequencing and Analysis Conference.

 

"If Rodney Dangerfield were to go to a genomics meeting, he would represent himself as the Y chromosome," Page quipped. "The Y chromosome has had a public relations problem for a long time."

 

Y's bad reputation, said Page, is based on the theory that it is unable to keep itself healthy by doing what alleles of X and the other chromosomes do: cross over and swap gene recipes with their partner. Y, stranded all by itself, gets stuck with any mutations that may have occurred in the copying process. As a result, researchers have recently argued that these accumulated mutations will probably make the Y completely useless in 10 million years.

 

But Page has had enough of this Y-bashing.

 

"We think the Y has found itself a way around this seemingly inevitable problem," he said.

 

Page described how his group at Whitehead (which includes two women, Tomoko Kuroda-Kawaguchi and Helen Skaletsky) and Rick Wilson and Bob Waterston at Washington University's genome sequencing center, came up with a surprising finding while sequencing the Y: big chunks of euchromatic sequence were over 99.9 percent identical to other sequences in this region. These duplicate sections were also palindromic, and occurred in the male-specific region, the part of the chromosome that contains a large number of testis-coding genes.

 

From this insight, the group hypothesized that the Y chromosome uses these sections as genomic correction tape to fold upon itself, recombine, and fix its mutations.

 

"There are sequences on the Y chromosome that are effectively functioning as alleles," Page said.

 

Page's collaborators also found these palindromic copy sections on the chimpanzee Y chromosome--which means that they are at least five million years old. In other words, if Page and colleagues are right, Y chromosome has been doing just fine correcting itself for millions of years-and isn't going to rot away any time soon.

 

Still, the theory poses questions: while the other chromosomes are recombine with new alleles in every generation, ensuring a certain amount of uniformity in the gene pool, each Y is only recombining with itself. So does that mean that Y chromosomes are diverging from one another?

 

Page said that there were "no clean answers at this point."

 

If the answer is yes, then it means than rather than a disappearing male, the human population may see increasing genetic diversity within the male of the species.

 

Page did not specify whether he planned to publish his findings with the Y-chromosome paper, which is due to come out in Nature within the next couple of months.