Selection at two sex-linked loci
Selection at two sex-linked loci
复制标题
在两个性别连锁位点进行选择
作者：
R. Owen
推导了两个性别连锁或单倍体位点的选择递归方程，每个位点有两个等位基因。利用吸收雄性配子频率的变换，得到只包含雌性配子频率的平衡方程。结果表明，当且仅当1 / 2 rf[x1x4(v11+v44)−x2x3(v22+v33)]w22 = 0时，配子平衡发生在几何平均生存力的一个平稳点，其中rf为雌性的重组分数，w22为双杂合子的生存力，x1, x2, x3， x4分别为雌性配子AB， AB， AB， AB的频率，v11, v22, v33， v44为相应的雄性生存力。因此，一般来说，连锁平衡既不是使平均生存力处于平稳点的充分条件，也不是必要条件，系统中总会存在一些连锁不平衡，无论是雌性还是雄性，或者两者都存在。对雌性的对称选择进行了一些详细的分析，结果表明，除非在雄性中也存在一种特殊类型的对称选择，否则只能发生不对称平衡。比较了性连锁位点和常染色体位点的搭便车效应，发现男性在常染色体位点没有重组的情况下，搭便车效应比性连锁位点强。
Recurrence equations are derived for selection at two sex-linked or haplodiploid loci, each with two alleles. Equilibrium equations containing only the female gametic frequencies are obtained by using a transformation that absorbs the male gametic frequencies. It is shown that gametic equilibria occur at a stationary point of the geometric mean viability if, and only if, ½rf[x1x4(v11+v44) − x2x3(v22+v33)]w22 = 0, where rf is the recombination fraction in females, w22 is the viability of the double heterozygote, x1, x2, x3, x4 are the frequencies of the female gametes AB, Ab, aB, ab respectively and v11, v22, v33, v44 are the corresponding male viabilities. Therefore, in general, linkage equilibrium is neither sufficient nor necessary for the mean viability to be at a stationary point and there will always be some linkage disequilibrium in the system, either in females or males or both. Symmetrical selection in females is analysed in some detail and it is shown that unless there is also a particular type of symmetrical selection in males then only asymmetrical equilibria can occur. The hitchhiking effect at sex-linked and autosomal loci is compared, and it is found that with no recombination in males at autosomal loci the effect can be stronger than at sex-linked loci.