The hitch-hiking effect of a favourable gene
The hitch-hiking effect of a favourable gene
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DOI：
10.1017/s0016672300014634
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发表时间：
2007-10-01
影响因子：
1.5
通讯作者：
Haigh, John
中科院分区：
文献类型：
--
作者：
Smith, John Maynard;Haigh, John
当群体中发生选择性有利的基因替换时，紧密相连的基因座将发生基因频率的变化。在中性多态性的情况下，平均杂合性将降低到随距取代基因座的距离而变化的程度。估计取代对中性多态性的总体影响；在总规模为 10(6) 或更多（也可能为 10(4) 或更多）的群体中，这种效应将比随机固定更重要。这可以解释为什么自然群体中的多态性程度并没有像考虑不同规模群体中突变和随机固定之间的平衡时所预期的那样变化。对于在连锁基因座上选择性维持的多态性，从长远来看，只有当它导致完全固定时，这个过程才重要。如果与取代位点处的选择系数相比，连接位点处的选择系数较小，则表明连接位点处完全固定的概率约为 exp (- Nc)，其中 c 是重组分数，N 是群体大小。由此可见，在大量群体中，顺反子中可以发生选择性取代，而不会消除同一顺反子中选择性维持的多态性。
When a selectively favourable gene substitution occurs in a population, changes in gene frequencies will occur at closely linked loci. In the case of a neutral polymorphism, average heterozygosity will be reduced to an extent which varies with distance from the substituted locus. The aggregate effect of substitution on neutral polymorphism is estimated; in populations of total size 10(6) or more (and perhaps of 10(4) or more), this effect will be more important than that of random fixation. This may explain why the extent of polymorphism in natural populations does not vary as much as one would expect from a consideration of the equilibrium between mutation and random fixation in populations of different sizes. For a selectively maintained polymorphism at a linked locus, this process will only be important in the long run if it leads to complete fixation. If the selective coefficients at the linked locus are small compared to those at the substituted locus, it is shown that the probability of complete fixation at the linked locus is approximately exp (- Nc), where c is the recombinant fraction and N the population size. It follows that in a large population a selective substitution can occur in a cistron without eliminating a selectively maintained polymorphism in the same cistron.