Further to “X chromosome: All in a days work for random processes whose junkpile just happens to function like an alien’s supercomputer,” some readers complained that the Y chromosome appears to have been slighted of late. Time to redress that.
Once again, from ScienceDaily
“The Y chromosome has lost 90 percent of the genes it once shared with the X chromosome, and some scientists have speculated that the Y chromosome will disappear in less than 5 million years,” said evolutionary biologist Melissa A. Wilson Sayres, a Miller Postdoctoral Fellow in the Department of Integrative Biology at the University of California, Berkeley, and lead author of the new analysis.
Some mammals have already lost their Y chromosome, though they still have males and females and reproduce normally. And last month, researchers reported shuffling some genes in mice to create Y-less males that could produce normal offspring, leading some commentators to wonder whether the chromosome is superfluous.
“Our study demonstrates that the genes that have been maintained, and those that migrated from the X to the Y, are important, and the human Y is going to stick around for a long while,” she said.
Note: Open access paper.
AbstractThe human Y chromosome exhibits surprisingly low levels of genetic diversity. This could result from neutral processes if the effective population size of males is reduced relative to females due to a higher variance in the number of offspring from males than from females. Alternatively, selection acting on new mutations, and affecting linked neutral sites, could reduce variability on the Y chromosome. Here, using genome-wide analyses of X, Y, autosomal and mitochondrial DNA, in combination with extensive population genetic simulations, we show that low observed Y chromosome variability is not consistent with a purely neutral model. Instead, we show that models of purifying selection are consistent with observed Y diversity. Further, the number of sites estimated to be under purifying selection greatly exceeds the number of Y-linked coding sites, suggesting the importance of the highly repetitive ampliconic regions. While we show that purifying selection removing deleterious mutations can explain the low diversity on the Y chromosome, we cannot exclude the possibility that positive selection acting on beneficial mutations could have also reduced diversity in linked neutral regions, and may have contributed to lowering human Y chromosome diversity. Because the functional significance of the ampliconic regions is poorly understood, our findings should motivate future research in this area. – Melissa A. Wilson Sayres, Kirk E. Lohmueller, Rasmus Nielsen. Natural Selection Reduced Diversity on Human Y Chromosomes. PLoS Genetics, 2014; 10 (1): e1004064 DOI: 10.1371/journal.pgen.1004064
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