Takahata N
National Institute of Genetics, Mishima, Japan.
Genetics. 1991 Oct;129(2):585-95. doi: 10.1093/genetics/129.2.585.
In a geographically structured population, the interplay among gene migration, genetic drift and natural selection raises intriguing evolutionary problems, but the rigorous mathematical treatment is often very difficult. Therefore several approximate formulas were developed concerning the coalescence process of neutral genes and the fixation process of selected mutations in an island model, and their accuracy was examined by computer simulation. When migration is limited, the coalescence (or divergence) time for sampled neutral genes can be described by the convolution of exponential functions, as in a panmictic population, but it is determined mainly by migration rate and the number of demes from which the sample is taken. This time can be much longer than that in a panmictic population with the same number of breeding individuals. For a selected mutation, the spreading over the entire population was formulated as a birth and death process, in which the fixation probability within a deme plays a key role. With limited amounts of migration, even advantageous mutations take a large number of generations to spread. Furthermore, it is likely that these mutations which are temporarily fixed in some demes may be swamped out again by non-mutant immigrants from other demes unless selection is strong enough. These results are potentially useful for testing quantitatively various hypotheses that have been proposed for the origin of modern human populations.
在一个具有地理结构的种群中，基因迁移、遗传漂变和自然选择之间的相互作用引发了有趣的进化问题，但严格的数学处理往往非常困难。因此，针对岛屿模型中中性基因的合并过程和选择突变的固定过程，人们开发了几个近似公式，并通过计算机模拟检验了它们的准确性。当迁移受到限制时，抽样中性基因的合并（或分歧）时间可以用指数函数的卷积来描述，就像在随机交配种群中一样，但它主要由迁移率和抽样所来自的deme数量决定。这个时间可能比具有相同繁殖个体数量的随机交配种群长得多。对于一个选择突变，其在整个种群中的传播被表述为一个生死过程，其中deme内的固定概率起着关键作用。在迁移量有限的情况下，即使是有利突变也需要大量世代才能传播开来。此外，除非选择足够强烈，否则这些在某些deme中暂时固定的突变很可能会再次被来自其他deme的非突变移民所淹没。这些结果对于定量检验为现代人类种群起源所提出的各种假设可能是有用的。
