Baird S J E
Institute of Cell Animal and Population Biology, The University of Edinburgh, Ashworth Laboratories, King's Buildings, West Mains Road, Edinburgh, EH9 3JT, United Kingdom.
Evolution. 1995 Dec;49(6):1038-1045. doi: 10.1111/j.1558-5646.1995.tb04431.x.
Fisher's method of junctions is used to investigate the degree of association between selected alleles in a cline, in the limit where there is divergence between very many genes. A computer model is used to simulate one of a pair of infinite demes that exchange individuals each generation. Selection is on haploids; it is additive and is equivalent to heterozygote disadvantage. Recombination is uniform over a single chromosome. A "critical value" of selection exists at equilibrium, below which loci act independently and above which they act in association (Barton 1983). Starting with secondary contact, simulation results contrast markedly with the equilibrium solution. The "critical value" is not apparent in the simulated clines, even after many generations. Rather, loci remain associated to some extent under all degrees of selection. The simulation is consistent with the equilibrium analysis in all other respects, and therefore indicates that under weak selection the approach to equilibrium is very slow. This is borne out by further numerical calculations. The slow approach to equilibrium enables us to estimate the time since contact between two demes under idealized conditions. Extending this work toward natural hybrid zones is discussed.
费希尔的交界方法用于研究渐变群中所选等位基因之间的关联程度，在众多基因存在分歧的极限情况下。使用计算机模型模拟一对无限种群中的一个，这两个种群每代交换个体。选择作用于单倍体；它是加性的，等同于杂合子劣势。重组在单个染色体上是均匀的。在平衡状态下存在一个选择的“临界值”，低于该值时基因座独立起作用，高于该值时它们协同起作用（巴顿，1983年）。从二次接触开始，模拟结果与平衡解形成显著对比。即使经过许多代，在模拟的渐变群中“临界值”也不明显。相反，在所有选择程度下基因座都在一定程度上保持关联。该模拟在所有其他方面都与平衡分析一致，因此表明在弱选择下达到平衡的过程非常缓慢。这一点通过进一步的数值计算得到了证实。达到平衡的缓慢过程使我们能够在理想化条件下估计两个种群接触后的时间。讨论了将这项工作扩展到自然杂交区的情况。
