The effects of inbreeding at loci with heterozygote advantage.
The effects of inbreeding at loci with heterozygote advantage.
复制标题
具有杂合子优势的基因座近交的影响。
作者：
W. G. Hill;A. Robertson
在 FISHER 和 WRIGHT 的早期研究中，有限规模种群内的选择理论受到了广泛关注。 KIMURA (1964) 回顾了基于连续模型的理论部分，在连续模型中，通常假设个体在小型封闭亚种群或品系内随机交配。在这种情况下，我们关心的是多个复制品系中单个基因的频率分布，或者等效地，同一品系中相同基因的频率分布。在本报告中，我们研究了有利于杂合个体的选择，在品系内随机交配，并且品系之间不发生选择或杂交。我们讨论的近交模型必须与另一种情况区分开来，这种情况在植物中可能更常见，在这种情况下，由于非随机交配，例如通过自交或混合自交和异交，近交发生在无限大的种群中。在后一种类型的模型中，选择也可能发生在亚系之间，并且在没有固定的情况下发生基因频率平衡不需要经常突变，而在我们的模型中是这样。阿拉德和他的同事最近对这些均衡情况进行了一些详细的分析。 JAIN 和 WORKMAN (1967) 回顾了他们对单基因座的许多结果，JAIN 和 ALLARD (1966) 给出了双基因座模型的分析。 REEVE (1955) 和 ROBERTSON (1962) 使用转移概率矩阵研究了只有少数个体的品系中的交配类型，研究了当没有品系间选择时小品系中杂合个体选择的影响。后者考虑了两种情况——首先，当突变和固定之间存在平衡时；其次，在没有突变的情况下，杂合性的数量以稳定的速度下降。在这两种情况中，关键因素被证明是平衡基因频率，这取决于两个纯合子的相对适应度。如果平衡频率超出 0.2 至 0.8 的范围，则选择可能会产生与通常预期相反的效果，并增加固定率。在本文中，我们将关注在已知初始基因频率的小品系中杂合子选择的中间阶段。选择可能会改变平均基因频率和杂合子的比例
INCE the early studies of FISHER and WRIGHT the theory of selection within populations of finite size has received much attention. KIMURA (1964) has reviewed the part of the theory that is based on continuous models in which it is usually assumed that individuals mate at random within small closed sub-populations or lines. In such a situation we are concerned with the distribution of the frequency of individual genes over many replicate lines, or, equivalently, the distribution of the frequency of identical genes within the same line. In this report we study selection favouring heterozygous individuals with random mating within lines and no selection or crossing occurring between lines. The model for inbreeding which we discuss must be distinguished from an alternative situation, perhaps more common in plants, in which inbreeding occurs within an infinitely large population as a result of non-random mating, for example by selfing or mixed selfing and outcrossing. In the latter type of model, selection also may occur between sublines and recurrent mutation is not required for equilibria of gene frequency to occur without fixation, whereas it is in our model. These equilibrium situations have been analysed recently in some detail by ALLARD and co-workers. Many of their results for single loci are reviewed by JAIN and WORKMAN (1967) and analysis of a two locus model is given by JAIN and ALLARD (1966). The effect of selection for heterozygous individuals in small lines when there is no between-line selection has been studied by REEVE (1955) using transition probability matrices for mating types in lines of only a few individuals, and by ROBERTSON (1962). The latter considered two situations-firstly when there is a balance between mutation and fixation and secondly when, in the absence of mutation, the amount of heterozygosis is declining at a steady rate. In both, the critical factor proved to be the equilibrium gene frequency, which depends on the relative fitness of the two homozygotes. If the equilibrium frequency lies outside the range 0.2 to 0.8 then selection may have an effect opposite to that usually expected and increase the rate of fixation. In the present paper we shall be concerned with the intermediate stages of selection for the heterozygote in small lines with a known initial gene frequency. Selection may alter the mean gene frequency and the proportion of heterozygotes