Human females have two of the same kind of sex chromosome (XX) while males have two distinct sex chromosomes (XY). Now new research indicates that the X chromosome may contribute heavily to sperm production in males — which sounds vaguely incestuous!!
But the news that females have always controlled and do control sperm production in males will not come as any great surprise to any teenager.
Jacob L Mueller, Helen Skaletsky, Laura G Brown, Sara Zaghlul, Susan Rock, Tina Graves, Katherine Auger, Wesley C Warren, Richard K Wilson and David C Page. Independent specialization of the human and mouse X chromosomes for the male germ line. Nature Genetics, 2013; DOI:10.1038/ng.2705
We compared the human and mouse X chromosomes to systematically test Ohno’s law, which states that the gene content of X chromosomes is conserved across placental mammals. First, we improved the accuracy of the human X-chromosome reference sequence through single-haplotype sequencing of ampliconic regions. The new sequence closed gaps in the reference sequence, corrected previously misassembled regions and identified new palindromic amplicons. Our subsequent analysis led us to conclude that the evolution of human and mouse X chromosomes was bimodal. In accord with Ohno’s law, 94–95% of X-linked single-copy genes are shared by humans and mice; most are expressed in both sexes. Notably, most X-ampliconic genes are exceptions to Ohno’s law: only 31% of human and 22% of mouse X-ampliconic genes had orthologs in the other species. X-ampliconic genes are expressed predominantly in testicular germ cells, and many were independently acquired since divergence from the common ancestor of humans and mice, specializing portions of their X chromosomes for sperm production.
PhysOrg writes:
Painstaking new analysis of the genetic sequence of the X chromosome—long perceived as the “female” counterpart to the male-associated Y chromosome—reveals that large portions of the X have evolved to play a specialized role in sperm production.
This surprising finding, reported by Whitehead Institute scientists in a paper published online this week in the journal Nature Genetics, is paired with another unexpected outcome: despite its reputation as the most stable chromosome of the genome, the X has actually been undergoing relatively swift change. Taken together, these results suggest that it’s time to reexamine the biological and medical importance of the X chromosome.
“We view this as the double life of the X chromosome,” says Whitehead Institute Director David Page, whose lab conducted this latest research.
“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 color blindness, hemophilia, and Duchenne’s muscular dystrophy,” Page adds. “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.”
Read more at: http://phys.org/news/2013-07-sex-chromosome-shocker-female-key.html#jCp
Tags: Nature Genetics, sex chromosomes, sperm production, X chromosome
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