Males' Y Chromosome Not in Decline

Jan. 14 -- WEDNESDAY, Jan. 13 (HealthDay News) -- The Y chromosome, found only in males, has evolved faster than expected in humans and chimpanzees over the past 6 million years since the two species emerged from a common ancestor, researchers report.

The new study challenges the widely held belief that the mammalian Y chromosome is slowly decaying or stagnating.

The Y chromosome is present in males (who have one Y and one X chromosome) but not in females (who have two X chromosomes).

"The region of the Y that is evolving the fastest is the part that plays a role in sperm production. The rest of the Y is evolving more like the rest of the genome, only a little bit faster," study first author Jennifer Hughes, of the Whitehead Institute for Biomedical Research in Cambridge, Mass., said in a news release from the Massachusetts Institute of Technology. Hughes is a postdoctoral researcher in the lab of Whitehead director David Page.

It had been believed that the human and chimp Y chromosomes would be highly similar. But this first comprehensive interspecies comparison of Y chromosomes revealed major differences in structure and gene content.

For example, the chimp Y chromosome has lost one-third to one-half of the human Y chromosome genes, which is a significant change in a relatively short period of evolutionary time. The changes in the Y chromosome are like a house undergoing continual renovation, one researcher explained.

"People are living in the house, but there's always some room that's being demolished and reconstructed. And this is not the norm for the genome as a whole," Whitehead director David Page said in the news release.

"This work clearly shows that the Y is pretty ingenious at using different tools than the rest of the genome to maintain diversity of genes. These findings demonstrate that our knowledge of the Y chromosome is still advancing," added Wes Warren, assistant director of the Washington University Genome Center, which was involved in the research.