Stephan W, Mitchell S J
Department of Zoology, University of Maryland, College Park 20742.
Genetics. 1992 Dec;132(4):1039-45. doi: 10.1093/genetics/132.4.1039.
We have estimated DNA sequence variation within and between two populations of Drosophila ananassae, using six-cutter restriction site variation at vermilion (v) and furrowed (fw). These two gene regions are located close to the centromere on the left and right X chromosome arms, respectively. In the fw region, no DNA polymorphism was detected within each population. In the v region, average heterozygosity per nucleotide was very low in both populations (pi = 0.0005 in the Burma population, and 0.0009 in the India population). These estimates are significantly lower than those from loci in more distal gene regions. The distribution of DNA polymorphisms between both populations was also striking. At fw, three fixed differences between the Burma and India populations were detected (two restriction site differences and one insertion/deletion of approximately 2 kb). At v, each DNA polymorphism in high frequency in the total sample was nearly fixed in one or the other population, although none of them reached complete fixation. The observed pattern of reduced variation within populations and fixed differences between populations appears to correlate with recombination rate. We conclude that recent hitchhiking associated with directional selection is the best explanation for this pattern. The data indicate that different selective sweeps have occurred in the two populations. The possible role of genetic hitchhiking in rapid population differentiation in gene regions of restricted recombination is discussed.
我们利用朱砂眼（v）和皱翅（fw）基因座上的六碱基切割限制位点变异，估算了拟果蝇两个种群内部及种群之间的DNA序列变异。这两个基因区域分别位于左、右X染色体臂靠近着丝粒的位置。在fw区域，每个种群内均未检测到DNA多态性。在v区域，两个种群中每个核苷酸的平均杂合度都非常低（缅甸种群中π = 0.0005，印度种群中π = 0.0009）。这些估计值显著低于来自更远端基因区域基因座的估计值。两个种群之间DNA多态性的分布也很显著。在fw基因座，检测到缅甸和印度种群之间存在三个固定差异（两个限制位点差异和一个约2 kb的插入/缺失）。在v基因座，总样本中高频出现的每个DNA多态性在一个或另一个种群中几乎固定，但均未达到完全固定。观察到的种群内变异减少和种群间固定差异的模式似乎与重组率相关。我们得出结论，与定向选择相关的近期搭便车效应是对这种模式的最佳解释。数据表明两个种群中发生了不同的选择性清除事件。本文讨论了遗传搭便车效应在重组受限基因区域快速种群分化中可能发挥的作用。
