The maintenance of genetic variability in two-locus models of stabilizing selection.
The maintenance of genetic variability in two-locus models of stabilizing selection.
复制标题
稳定选择的双基因座模型中遗传变异的维持。
DOI：
10.1093/genetics/122.1.235
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发表时间：
1989
期刊：
影响因子：
3.3
通讯作者：
T. Nagylaki
中科院分区：
文献类型：
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作者：
T. Nagylaki
研究了稳定选择下两个双等位基因座遗传变异性的维持。世代是离散且不重叠的；交配是随机的；不存在突变和随机遗传漂变；选择仅通过生存能力差异进行。基因型值的测定纯粹是累加性的。适应度函数在双杂合子的值处具有其最佳值，并从其最佳值单调对称地减小，但在其他方面是任意的。所得的适应度方案与对称生存力模型相同。忽略连锁不平衡，但结果在其他方面是准确的。所有平衡点都找到了明确的公式，并从它们的存在性和稳定性中推导出了明确的条件。提出了六种可能的全球收敛模式的完整分类。除了对称平衡（两个位点基因频率均为 1/2）外，还可能存在一对不对称平衡；后者通常（但并非总是）不稳定。如果主要基因座与次要基因座的效应之比超过某一临界值，则两个基因座都将具有稳定的多态性。如果次要基因座的选择较弱，则适应度函数在最佳值附近下降得越快，该临界值就越低；对于快速下降的适应度函数，临界值接近于 1。如果适应度函数在最佳状态下是平滑的，则仅当主要基因座的选择较强时，两个基因座才存在稳定的多态性。
The maintenance of genetic variability at two diallelic loci under stabilizing selection is investigated. Generations are discrete and nonoverlapping; mating is random; mutation and random genetic drift are absent; selection operates only through viability differences. The determination of the genotypic values is purely additive. The fitness function has its optimum at the value of the double heterozygote and decreases monotonically and symmetrically from its optimum, but is otherwise arbitrary. The resulting fitness scheme is identical to the symmetric viability model. Linkage disequilibrium is neglected, but the results are otherwise exact. Explicit formulas are found for all the equilibria, and explicit conditions are derived fro their existence and stability. A complete classification of the six possible global convergence patterns is presented. In addition to the symmetric equilibrium (with gene frequency 1/2 at both loci), a pair of unsymmetric equilibria may exist; the latter are usually, but not always, unstable. If the ratio of the effect of the major locus to that of the minor one exceeds a critical value, both loci will be stably polymorphic. If selection is weak at the minor locus, the more rapidly the fitness function decreases near the optimum, the lower is this critical value; for rapidly decreasing fitness functions, the critical value is close to one. If the fitness function is smooth at the optimum, then a stable polymorphism exists at both loci only if selection is strong at the major locus.