Hvilsom C, Qian Y, et. al. (2012) “Extensive X-linked adaptive evolution in central chimpanzees.” PNAS
They analyzed the amount of diversity on autosomes and the X chromosomes in exons in chimpanzees. They showed higher diversity in chimpanzees than in humans, in line with earlier studies. Using the DFE-alpha approach they showed that strong selection (Nes > 100) is slightly elevated on the X chromosome (though they didn’t test for significance, however the Ne of the X should be lower than autosomes, so this is a strong sign of differences in selection). Using two different McDonald-Kreitman based tests they show no evidence for positive selection on autosomes but some on the X chromosome (38% from DFE-alpha). The saw no evidence for selective sweeps in windows in the X chromosome however, they suggest the difference in alpha is caused by fixations of novel recessive mutations being fixed. They also show very reduced coding polymorphism on the X chromosome compared to autosomes, showing faster X evolution caused by positive selection.
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