Payseur Bret A, Nachman Michael W
Department of Ecology and Evolutionary Biology, Biosciences West Building, University of Arizona, Tucson, AZ 85721, USA.
Gene. 2002 Oct 30;300(1-2):31-42. doi: 10.1016/s0378-1119(02)00849-1.
Theoretical and empirical work indicates that patterns of neutral polymorphism can be affected by linked, selected mutations. Under background selection, deleterious mutations removed from a population by purifying selection cause a reduction in linked neutral diversity. Under genetic hitchhiking, the rise in frequency and fixation of beneficial mutations also reduces the level of linked neutral polymorphism. Here we review the evidence that levels of neutral polymorphism in humans are affected by selection at linked sites. We then discuss four approaches for distinguishing between background selection and genetic hitchhiking based on (i) the relationship between polymorphism level and recombination rate for neutral loci with high mutation rates, (ii) relative levels of variation on the X chromosome and the autosomes, (iii) the frequency distribution of neutral polymorphisms, and (iv) population-specific patterns of genetic variation. Although the evidence for selection at linked sites in humans is clear, current methods and data do not allow us to clearly assess the relative importance of background selection and genetic hitchhiking in humans. These results contrast with those obtained for Drosophila, where the signals of positive selection are stronger.
理论和实证研究表明，中性多态性模式会受到连锁的、被选择的突变的影响。在背景选择下，通过纯化选择从种群中清除的有害突变会导致连锁中性多样性的降低。在基因搭便车现象中，有益突变的频率上升和固定也会降低连锁中性多态性的水平。在此，我们综述了人类中性多态性水平受连锁位点选择影响的证据。然后，我们讨论了四种区分背景选择和基因搭便车现象的方法，这些方法基于：（i）高突变率中性位点的多态性水平与重组率之间的关系；（ii）X染色体和常染色体上变异的相对水平；（iii）中性多态性的频率分布；以及（iv）群体特异性的遗传变异模式。尽管人类连锁位点存在选择的证据确凿，但目前的方法和数据尚无法让我们清楚地评估背景选择和基因搭便车现象在人类中的相对重要性。这些结果与在果蝇中获得的结果形成对比，果蝇中的正选择信号更强。
