遗传变异数据中的古代平衡多态性足迹
Footprints of ancient balanced polymorphisms in genetic variation data
摘要：
当长期存在时，平衡选择可以导致跨物种多态性，这些多态性由两个或多个相同的物种共享。在这种情况下，所选位点的基因谱系是按等位基因而不是按物种聚类的，而且由于连锁，附近的中性位点也有不寻常的谱系。虽然很明显，这种情况下，应导致可辨别的足迹在遗传变异数据，特别是存在额外的中性多态性物种之间共享和固定差异的情况下，效果仍然很差的特点。我们专注于一个单一的网站下的情况下，长期平衡的选择，并得出近似值的数据是敏感的跨物种多态性的总结：携带大部分的信号的片段的长度，预期数量的共享中性SNP的片段和模式之间的等位基因协会。古代平衡选择的合并模拟证实了我们近似值的准确性。我们进一步表明，对于人类和黑猩猩，更普遍的是，对于遗传多样性〈动〉性<动>水平较低的物种对，我们关注的遗传变异模式极不可能由中性复发突变产生，因此这些统计数据是特异性的，也是敏感的。我们讨论了我们的研究结果的影响，在猿和其他类群的古代平衡选择的基因组扫描的设计和解释。
英文摘要：
When long-lived, balancing selection can lead to trans-species polymorphisms that are shared by two or more species identical by descent. In this case, the gene genealogies at the selected sites cluster by allele instead of by species and, because of linkage, nearby neutral sites also have unusual genealogies. Although it is clear that this scenario should lead to discernible footprints in genetic variation data, notably the presence of additional neutral polymorphisms shared between species and the absence of fixed differences, the effects remain poorly characterized. We focus on the case of a single site under long-lived balancing selection and derive approximations for summaries of the data that are sensitive to a trans-species polymorphism: the length of the segment that carries most of the signals, the expected number of shared neutral SNPs within the segment and the patterns of allelic associations among them. Coalescent simulations of ancient balancing selection confirm the accuracy of our approximations. We further show that for humans and chimpanzees, and more generally for pairs of species with low genetic diversity levels, the patterns of genetic variation on which we focus are highly unlikely to be generated by neutral recurrent mutations, so these statistics are specific as well as sensitive. We discuss the implications of our results for the design and interpretation of genome scans for ancient balancing selection in apes and other taxa.
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