Researchers have made the surprising finding that the "female" X chromosome may have an important function in sperm production.
Women have two X chromosomes and men have an X and Y chromosome. This study found that large portions of the X chromosome have evolved to play a specialized role in producing sperm.
And despite its reputation as the most stable chromosome of the genome, the X chromosome has actually been undergoing relatively rapid changes, according to the study published online July 21 in the journal Nature Genetics.
Taken together, these two findings suggest that it's time to re-examine the biological and medical importance of the X chromosome, said the researchers at the Whitehead Institute for Biomedical Research in Cambridge, Mass.
"We view this as the double life of the X chromosome," Whitehead director David Page said in an institute news release.
"The X is the most famous, most intensely studied chromosome in all of human genetics. And the story of the X has been the story of X-linked recessive diseases, such as colour blindness, hemophilia, and Duchenne's muscular dystrophy," Page noted. "But there's another side to the X, a side that is rapidly evolving and seems to be attuned to the reproductive needs of males."
In the study, the researchers compared mouse and human X chromosomes and found that they had nearly 95% of their X-linked, single-copy genes in common. Nearly all these genes are expressed in both sexes.
But the study also identified about 340 genes that are not shared between mice and humans. Most of these genes are active almost exclusively in testicular germ cells where they likely contribute to sperm production.
"These genes are more likely to have roles in diseases that are related to reproduction, infertility, perhaps even testis cancer. There's a whole other book to be written about this aspect of the X," Page noted in the news release.
The US National Library of Medicine has more about chromosomes.