The study's lead author evolutionary biologist Melissa A. Wilson Sayres
from the University of California, Berkeley said that 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. Some mammals have already lost their Y chromosome, though they still have males and females and reproduce normally.
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," the researcher said.
The UC Berkeley researchers demonstrated that if fewer males were the only cause of the low variability, it would mean that fewer than 1 in 4 males throughout history had passed on their Y chromosome each generation. Variations in other human chromosomes, including the X chromosome, make this an unlikely scenario.
Instead, they showed that the low variation can be explained by intense natural selection, that is, a strong evolutionary pressure to weed out bad mutations that ended up trimming the chromosome down to its essentials.
The study was published in journal PLOS Genetics.
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