Long live the Y?

From Boston, Mass., at the Genome Sequencing and Analysis conference

Rumors of the human Y chromosome’s eventual death may be exaggerated. David Page of the Whitehead Institute for Biomedical Research in Cambridge, Mass., and his colleagues have identified a means by which the Y chromosome may forestall, or at least delay, the gradual degradation that some biologists argue will ultimately delete it from the human genome.

In the Feb. 28 Nature, two Australian scientists summarized recent research showing that the human Y chromosome gradually accumulates mutations that deactivate its few genes. Non-sex chromosome pairs have a chance to replace mutation-ridden sections by swapping DNA with the each other. But most of the Y is unable to exchange DNA with its partner, the X chromosome. “At the present rate of decay, the Y chromosome will self-destruct in around 10 million years,” the two researchers said.

Page’s group isn’t so sure. These researchers have sequenced all the DNA on the Y and discovered that many of its genes have neighboring doubles. A gene and its copy often form DNA palindromes, in which a gene’s DNA sequence is followed by nearly the same sequence, but in reverse. (Palindromes in literature are words or phrases that read the same forward or backward, such as, “Was it a rat I saw?”).

Further scrutiny of the Y palindromes led the researchers to conclude that each gene and its backward copy are so similar in sequence that they must regularly exchange DNA in a novel form of the recombination observed in nonsex chromosomes.

“There is, in fact, intense recombination within the arms of the palindrome,” says Page. “It really changes the way we think about the Y chromosome.” He speculates that the palindromes enable the human Y chromosome to constantly repair mutations, staving off its own degradation.

“It’s a great story,” comments Eric Green of the National Human Genome Research Institute in Bethesda, Md. He suggests that researchers should look for such palindromes in sex chromosomes of other animals


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