The amount of DNA sequence variability in a genomic region is often positively correlated with its rate of crossing over (CO) []. This pattern is caused by selection acting on linked sites, which reduces genetic variability and biases the frequency distribution of segregating variants toward more rare variants than are expected without selection (skew). These effects may involve the spread of beneficial mutations (selective sweeps [SSWs]), the elimination of deleterious mutations (background selection [BGS]), or both, and are expected to be stronger with lower CO rates []. However, in a recent study of human populations, the skew was reduced in the lowest CO regions compared with regions with somewhat higher CO rates []. A low skew in very low CO regions, compared with theoretical predictions, is seen in the population genomic studies of described here and in other species. Here, we propose an explanation for lower than expected skew in low CO regions, and validate it using computer simulations; explanations for higher skew with higher CO rates, as in , will be explored elsewhere. Partially recessive, linked deleterious mutations can increase neutral variability when the product of the effective population size () and the selection coefficient against homozygous carriers of mutations () is ≤1, i.e., there is associative overdominance (AOD) rather than BGS []. AOD can operate in low CO regions, producing a lower skew than in its absence. This opens up a new perspective on how selection affects patterns of variability at linked sites.

中文翻译：

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低重组率基因组区域的遗传变异模式

基因组区域中 DNA 序列变异性的量通常与其交叉率 (CO) 呈正相关。这种模式是由作用于连锁位点的选择引起的，这减少了遗传变异性，并使分离变体的频率分布偏向于比没有选择时预期的更罕见的变体（偏斜）。这些效应可能涉及有益突变的传播（选择性清除 [SSW]）、有害突变的消除（背景选择 [BGS]）或两者兼而有之，并且预计随着 CO 率降低而增强 []。然而，在最近的一项针对人群的研究中，与二氧化碳排放率较高的地区相比，二氧化碳排放量最低的地区的偏差有所减小。与理论预测相比，在极低二氧化碳区域的偏差较低，在此处描述的群体基因组研究和其他物种中可见。在这里，我们提出了对低二氧化碳地区低于预期偏差的解释，并使用计算机模拟对其进行验证；对于较高的 CO 浓度导致较高偏差的解释（如 中），将在其他地方进行探讨。当有效群体规模（）和针对突变纯合携带者的选择系数（）的乘积≤1时，部分隐性连锁有害突变可以增加中性变异，即存在关联过度显性（AOD）而不是BGS[]。 AOD 可以在二氧化碳含量较低的地区运行，产生的偏差比没有它时更低。这为选择如何影响链接位点的变异模式开辟了新的视角。