Tachida H
National Institute of Genetics, Shizuoka-ken, Japan.
Genetics. 1991 May;128(1):183-92. doi: 10.1093/genetics/128.1.183.
As a nearly neutral mutation model, the house-of-cards model is studied in finite populations using computer simulations. The distribution of the mutant effect is assumed to be normal. The behavior is mainly determined by the product of the population size, N, and the standard deviation, sigma, of the distribution of the mutant effect. If 4N sigma is large compared to one, a few advantageous mutants are quickly fixed in early generations. Then most mutation becomes deleterious and very slow increase of the average selection coefficient follows. It takes very long for the population to reach the equilibrium state. Substitutions of alleles occur very infrequently in the later stage. If 4N sigma is the order of one or less, the behavior is qualitatively similar to that of the strict neutral case. Gradual increase of the average selection coefficient occurs and in generations of several times the inverse of the mutation rate the population almost reaches the equilibrium state. Both advantageous and neutral (including slightly deleterious) mutations are fixed. Except in the early stage, an increase of the standard deviation of the distribution of the mutant effect decreases the average heterozygosity. The substitution rate is reduced as 4N sigma is increased. Three tests of neutrality, one using the relationship between the average and the variance of heterozygosity, another using the relationship between the average heterozygosity and the average number of substitutions and Watterson's homozygosity test are applied to the consequences of the present model. It is found that deviation from the neutral expectation becomes apparent only when 4N sigma is more than two. Also a simple approximation for the model is developed which works well when the mutation rate is very small.
作为一种近似中性的突变模型，使用计算机模拟在有限种群中研究了纸牌屋模型。假定突变效应的分布呈正态分布。其行为主要由种群大小N与突变效应分布的标准差σ的乘积决定。如果4Nσ比1大得多，一些有利突变体在早期世代中很快就会被固定下来。然后大多数突变变得有害，平均选择系数的增加非常缓慢。种群达到平衡状态需要很长时间。后期等位基因的替换非常罕见。如果4Nσ为1或更小的量级，其行为在定性上与严格中性情况相似。平均选择系数会逐渐增加，在几代突变率的倒数时间内，种群几乎达到平衡状态。有利突变和中性突变（包括轻度有害突变）都会被固定下来。除了在早期阶段，突变效应分布的标准差增加会降低平均杂合度。替换率随着4Nσ的增加而降低。将三种中性检验应用于本模型的结果，一种使用杂合度的平均值与方差之间的关系，另一种使用平均杂合度与平均替换数之间的关系以及沃特森纯合度检验。结果发现，只有当4Nσ大于2时，与中性预期的偏差才会明显。还针对该模型开发了一种简单的近似方法，当突变率非常小时效果很好。
