Men and women: The differences are in the genes
“This tells us that neighborhoods matter,” Carrel said. “Genes on the X chromosome evolved in five sequential segments or layers. The older segments have fewer genes that escape inactivation than those that developed later in the chromosome’s evolutionary path. This suggests that, as the human species continues to evolve, more and more of the genes that are escaping inactivation may lose their ability to do so.”
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“Using primary skin cells, she compared gene expression between the X chromosome and the inactive chromosome for 94 genes spanning the X chromosome in 40 human samples. She found that only 65 percent of the genes were inactive in all samples. Twenty percent were inactivated in some samples and not in others, and 15 percent escaped inactivation in all samples. In addition, many of those from the inactive X that were expressed were only partially expressed.”
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“The data also suggests that the female genome now differs from the male genome in at least four ways. First, previous studies had shown that the Y chromosome gives males several genes that are absent in the female. Second, this study shows the fact that some genes on the inactive X are expressed means that about 15 percent of the genes are expressed at higher levels in females than in males. Third, this study also shows an additional 10 percent of genes on the inactive X show variable expression levels in females, whereas men have only a single copy of these genes. And finally, scientists had already known that random nature of X-inactivation shows that females, but not males, are mosaics of two cell populations with respect to X-linked gene expression.”
Posted by fly at 05:03 PM