Whitlock Michael C
Department of Zoology, University of British Columbia, Vancouver, Canada.
Genetics. 2003 Jun;164(2):767-79. doi: 10.1093/genetics/164.2.767.
New alleles arising in a population by mutation ultimately are either fixed or lost. Either is possible, for both beneficial and deleterious alleles, because of stochastic changes in allele frequency due to genetic drift. Spatially structured populations differ from unstructured populations in the probability of fixation and the time that this fixation takes. Previous results have generally made many assumptions: that all demes contribute to the next generation in exact proportion to their current sizes, that new mutations are beneficial, and that new alleles have additive effects. In this article these assumptions are relaxed, allowing for an arbitrary distribution among demes of reproductive success, both beneficial and deleterious effects, and arbitrary dominance. The effects of population structure can be expressed with two summary statistics: the effective population size and a variant of Wright's F(ST). In general, the probability of fixation is strongly affected by population structure, as is the expected time to fixation or loss. Population structure changes the effective size of the species, often strongly downward; smaller effective size increases the probability of fixing deleterious alleles and decreases the probability of fixing beneficial alleles. On the other hand, population structure causes an increase in the homozygosity of alleles, which increases the probability of fixing beneficial alleles but somewhat decreases the probability of fixing deleterious alleles. The probability of fixing new beneficial alleles can be simply described by 2hs(1 - F(ST))N(e)/N(tot), where hs is the change in fitness of heterozygotes relative to the ancestral homozygote, F(ST) is a weighted version of Wright's measure of population subdivision, and N(e) and N(tot) are the effective and census sizes, respectively. These results are verified by simulation for a broad range of population structures, including the island model, the stepping-stone model, and a model with extinction and recolonization.
通过突变在种群中产生的新等位基因最终要么被固定，要么丢失。由于遗传漂变导致等位基因频率的随机变化，这两种情况对有益和有害等位基因来说都是可能的。空间结构种群在固定概率和固定所需时间方面与非结构种群不同。先前的结果通常做了许多假设：所有deme对下一代的贡献与其当前大小精确成比例，新突变是有益的，并且新等位基因具有加性效应。在本文中，这些假设被放宽，允许在deme之间存在任意的繁殖成功率分布、有益和有害效应以及任意的显性情况。种群结构的影响可以用两个汇总统计量来表示：有效种群大小和赖特F(ST)的一个变体。一般来说，固定概率受到种群结构的强烈影响，固定或丢失的预期时间也是如此。种群结构改变了物种的有效大小，通常会大幅减小；较小的有效大小增加了固定有害等位基因的概率，降低了固定有益等位基因的概率。另一方面，种群结构导致等位基因纯合性增加，这增加了固定有益等位基因的概率，但在一定程度上降低了固定有害等位基因的概率。固定新有益等位基因的概率可以简单地描述为2hs(1 - F(ST))N(e)/N(tot)，其中hs是杂合子相对于祖先纯合子的适合度变化，F(ST)是赖特种群细分度量的加权版本，N(e)和N(tot)分别是有效大小和普查大小。这些结果通过对广泛的种群结构进行模拟得到了验证，包括岛屿模型、跳板模型以及具有灭绝和重新定殖的模型。
