Ayala F J, Tracey M L, Barr L G, McDonald J F, Pérez-Salas S
Genetics. 1974 Jun;77(2):343-84. doi: 10.1093/genetics/77.2.343.
We have studied genetic variation at 30-32 loci coding for enzymes in natural populations of five species of Drosophila. The average proportion of heterozygous loci per individual is 17.7 +/- 0.4%. The average proportion of polymorphic loci per population is 69.2 +/- 2.6% or 49.8 +/- 2.2%, depending on what criterion of polymorphism is used. The following generalizations are advanced: (1) The amount of genetic polymorphism varies considerably from locus to locus. (2) At a given locus, populations of the same species are very similar in the amount and pattern of genetic variation. (3) However, at some loci large differences sometimes occur between local populations of the same species. (4) The amount of variation at a given locus is approximately the same in all five species. (5) When different species are compared, the pattern of the variation is either essentially identical or totally different at a majority of loci. We have tested the hypothesis that protein polymorphisms are selectively neutral by examining four predictions derived from the hypothesis. Our results are at variance with every one of the predictions. We have measured the amount of genetic differentiation, D, between taxa of various degrees of evolutionary divergence. The average value of D is 0.033 for local populations, 0.228 for subspecies, 0.226 for semispecies, 0.538 for sibling species, and 1.214 for morphologically distinguishable species. Our results indicate that a substantial degree of genetic differentiation (22.8 allelic substitutions for every 100 loci) occurs between allopatric populations that have diverged to the point where they might become different species if they were to become sympatric. However, very little additional genetic change is required for the development of complete reproductive isolation. After the speciation process is completed, species continue to diverge genetically from each other.
我们研究了果蝇五个物种自然种群中30 - 32个编码酶的基因座的遗传变异。每个个体杂合基因座的平均比例为17.7±0.4%。每个种群多态基因座的平均比例为69.2±2.6%或49.8±2.2%，这取决于所使用的多态性标准。得出以下一般性结论：(1)遗传多态性的数量在不同基因座之间差异很大。(2)在给定基因座上，同一物种的种群在遗传变异的数量和模式上非常相似。(3)然而，在某些基因座上，同一物种的局部种群之间有时会出现很大差异。(4)在所有五个物种中，给定基因座的变异量大致相同。(5)当比较不同物种时，在大多数基因座上，变异模式要么基本相同，要么完全不同。我们通过检验从该假设推导的四个预测，来测试蛋白质多态性是选择性中性的这一假设。我们的结果与每一个预测都不一致。我们测量了不同进化分歧程度的分类群之间的遗传分化量D。局部种群的D平均值为0.033，亚种为0.228，半种为0.226，同胞种为0.538，形态上可区分的物种为1.214。我们的结果表明，在异地种群之间发生了相当程度的遗传分化（每100个基因座有22.8个等位基因替代），这些种群已经分化到如果它们变成同域分布就可能成为不同物种的程度。然而，完全生殖隔离的发展只需要很少的额外遗传变化。在物种形成过程完成后，物种继续在遗传上彼此分化。
