Recombination and hitchhiking of deleterious alleles

When new advantageous alleles arise and spread within a population, deleterious alleles at neighbouring loci can hitchhike alongside them and spread to fixation in areas of low recombination, introducing a fixed mutation load. We use branching processes and diffusion equations to calculate the probability that a deleterious allele hitchhikes and fixes alongside an advantageous mutant. As expected, the probability of fixation of a deleterious hitchhiker rises with the selective advantage of the sweeping allele and declines with the selective disadvantage of the deleterious hitchhiker. We then use computer simulations of a genome with an infinite number of loci to investigate the increase in load after an advantageous mutant is introduced. We show that the appearance of advantageous alleles on genetic backgrounds loaded with deleterious alleles has two potential effects: it can fix deleterious alleles and also facilitate the persistence of recombinant lineages that happen to occur. The latter i...当新的有利等位基因（advantageous alleles）在种群内出现并扩散时，邻近基因座（neighbouring loci）上的有害等位基因（deleterious alleles）可与其一同发生遗传搭车（hitchhike），并在低重组区域扩散至固定（fixation）状态，进而引入固定突变负荷（mutation load）。我们采用分支过程（branching processes）与扩散方程（diffusion equations），计算有害等位基因随有利突变发生遗传搭车并最终固定的概率。正如预期，有害搭车等位基因的固定概率随该正向选择清扫的有利等位基因的选择优势（selective advantage）升高而上升，随自身选择劣势（selective disadvantage）升高而下降。随后我们对拥有无限数量基因座的基因组开展计算机模拟（computer simulations），以探究有利突变引入后种群突变负荷的变化情况。研究表明，在携带有害等位基因的遗传背景（genetic backgrounds）上出现的有利等位基因，会产生两种潜在效应：一是可使有害等位基因发生固定，二是可促进偶然出现的重组谱系（recombinant lineages）的存续。后者即……