Background selection describes the reduction in neutral diversity caused by selection against deleterious alleles at other loci. It is typically assumed that the purging of deleterious alleles affects linked neutral variants, and indeed simulations typically only treat a genomic window. However, background selection at unlinked loci also depresses neutral diversity. In agreement with previous analytical approximations, in our simulations of a human-like genome with a realistically high genome-wide deleterious mutation rate, the effects of unlinked background selection exceed those of linked background selection. Background selection reduces neutral genetic diversity by a factor that is independent of census population size. Outside of genic regions, the strength of background selection increases with the mean selection coefficient, contradicting the linked theory but in agreement with the unlinked theory. Neutral diversity within genic regions is fairly independent of the strength of selection. Deleterious genetic load among haploid individuals is underdispersed, indicating non-independent evolution of deleterious mutations. Empirical evidence for underdispersion was previously interpreted as evidence for global epistasis, but we recover it from a non-epistatic model.

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来自未连锁位点的背景选择导致有害突变的非独立进化

背景选择描述了由于对其他位点的有害等位基因的选择而导致的中性多样性的减少。通常假设有害等位基因的清除会影响相关的中性变体，并且实际上模拟通常只处理基因组窗口。然而，未连锁基因座的背景选择也会抑制中性多样性。与之前的分析近似一致，在我们对具有实际高全基因组有害突变率的类人基因组的模拟中，未关联背景选择的影响超过了关联背景选择的影响。背景选择通过与人口普查人口规模无关的因素减少中性遗传多样性。在基因区域之外，背景选择的强度随着平均选择系数的增加而增加，这与关联理论相矛盾，但与非关联理论一致。基因区域内的中性多样性完全独立于选择的强度。单倍体个体中的有害遗传负荷分散不足，表明有害突变的非独立进化。不分散的经验证据以前被解释为全局上位性的证据，但我们从非上位模型中恢复了它。