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Researchers Publish Detailed Analysis of Y Chromosome Sequence

NEW YORK, June 20 - Large chunks of the Y chromosome read the same forward and backwards, providing it with a mechanism to maintain intact without a partner. This is just one result from two extensive analyses of the Y chromosome sequence, published yesterday in the journal Nature.

 

Researchers from the Whitehead Institute and the Department of Biology at MIT, the GenomeSequencingCenter at Washington University School of Medicine, and the AcademicMedicalCenter in Amsterdam, the Netherlands, found that the Y's 23 million base pairs of euchromatin contain three classes of sequences that harbor all of its 156 known transcription units. 78 of these encode proteins - though only 27 different ones.

 

Once class of sequence, called "X-transposed," appears to have moved over from the X chromosome within the last few million years and still bears about 99 percent identity to the corresponding X sequences. The second class, dubbed "X-degenerate," is more distantly related to the X chromosome and seems to derive from an ancient common ancestor of both X and Y. Finally, a series of eight large palindromic sequences - sequences that read the same in either direction -- makes up the third class, called "ampliconic."

 

These palindromes can undergo a form of recombination called gene conversion, where one arm of the palindrome "converts" its counterpart to a copy of itself - a way for the Y-chromosome to prevent its sequence from degenerating. The scientists found this mechanism to occur both in humans and in great apes.

 

Their analysis, the researchers say, may help understand the genetic basis of male infertility, as well as a female chromosomal disorder called Turner syndrome, where one X chromosome is missing.

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