Mallet J, Barton N
Department of Entomology, Mississippi State University, Mississippi 39762.
Genetics. 1989 Aug;122(4):967-76. doi: 10.1093/genetics/122.4.967.
Frequency-dependent selection against rare forms can maintain clines. For weak selection, s, in simple linear models of frequency-dependence, single locus clines are stabilized with a maximum slope of between square root of s/square root of 8 sigma and square root of s/square root of 12 delta, where sigma is the dispersal distance. These clines are similar to those maintained by heterozygote disadvantage. Using computer simulations, the weak-selection analytical results are extended to higher selection pressures with up to three unlinked genes. Graphs are used to display the effect of selection, migration, dominance, and number of loci on cline widths, speeds of cline movements, two-way gametic correlations ("linkage disequilibria"), and heterozygote deficits. The effects of changing the order of reproduction, migration, and selection, are also briefly explored. Epistasis can also maintain tension zones. We show that epistatic selection is similar in its effects to frequency-dependent selection, except that the disequilibria produced in the zone will be higher for a given level of selection. If selection consists of a mixture of frequency-dependence and epistasis, as is likely in nature, the error made in estimating selection is usually less than twofold. From the graphs, selection and migration can be estimated using knowledge of the dominance and number of genes, of gene frequencies and of gametic correlations from a hybrid zone.
针对稀有形态的频率依赖选择可以维持渐变群。对于弱选择（s），在频率依赖的简单线性模型中，单基因座渐变群得以稳定，其最大斜率介于√s/√8σ与√s/√12δ之间，其中σ是扩散距离。这些渐变群类似于由杂合子劣势维持的渐变群。通过计算机模拟，将弱选择分析结果扩展到了具有多达三个不连锁基因的更高选择压力情况。使用图表来展示选择、迁移、显性以及基因座数量对渐变群宽度、渐变群移动速度、双向配子相关性（“连锁不平衡”）和杂合子亏缺的影响。还简要探讨了改变繁殖、迁移和选择顺序的影响。上位性也可以维持张力带。我们表明，上位性选择的效果与频率依赖选择相似，只是在给定选择水平下，该区域产生的不平衡会更高。如果选择由频率依赖和上位性混合组成，这在自然界中很可能是这样，那么估计选择时所产生的误差通常小于两倍。从图表中，可以利用来自杂交区的显性和基因数量、基因频率以及配子相关性的知识来估计选择和迁移。
