Hilton Holly, Kliman Richard M, Hey Jody
Rutgers University, Nelson Labs, P.O. Box 1059, Piscataway, New Jersey, 08855-1059.
Evolution. 1994 Dec;48(6):1900-1913. doi: 10.1111/j.1558-5646.1994.tb02222.x.
Several studies of intraspecific and interspecific DNA sequence variation from Drosophila loci have revealed a pattern of low intraspecific variation from genomic regions of low recombination. The mechanisms consistently invoked to explain these patterns are the selective sweep of advantageous mutations together with genetic hitchhiking of linked loci. To examine the effect of selective sweeps on genetic divergence during speciation, we studied two loci in different genomic regions thought to be subject to selective sweeps. We obtained DNA sequences from 1.1kb pair portions of the fourth chromosome locus cubitus interruptus Dominant (ci ) and from the asense locus near the telomere of the X chromosome. At ci , we found very low variation among multiple lines of Drosophila mauritiana and D. sechellia. This finding is consistent with an earlier report of very low variation in D. melanogaster and D. simulans at ci and supports the conclusion of selective sweeps and genetic hitchhiking on the nonrecombining fourth chromosome. The pattern of variation found at asense suggests that a selective sweep has occurred recently at the tip of the X chromosome in D. simulans, but not in D. melanogaster or D. mauritiana. The data from ci and asense are compared with data from three X chromosome loci (period, zeste, and yolk protein 2) that experience normal levels of recombination. By examining estimated genealogies and the rates at which different classes of mutations have accumulated, we conclude that selective sweeps are common occurrences on the fourth chromosome but less common near the tip of the X chromosome. An interesting pattern of low variation at ci among D. simulans, D. mauritiana, and D. sechellia suggests that a selective sweep may have occurred among these forms even after divergence into separate species had begun.
多项针对果蝇基因座的种内和种间DNA序列变异的研究揭示了一种模式：重组率低的基因组区域内种内变异较低。一直被用来解释这些模式的机制是有利突变的选择性清除以及连锁基因座的遗传搭便车效应。为了研究物种形成过程中选择性清除对遗传分化的影响，我们研究了不同基因组区域中被认为受到选择性清除的两个基因座。我们获得了第四条染色体基因座间断肘脉显性（ci）1.1千碱基对部分的DNA序列，以及X染色体端粒附近的无义基因座的DNA序列。在ci基因座，我们发现毛里求斯果蝇和塞舌尔果蝇多个品系间的变异非常低。这一发现与之前关于黑腹果蝇和拟果蝇在ci基因座变异极低的报道一致，并支持了在不发生重组的第四条染色体上存在选择性清除和遗传搭便车效应的结论。在无义基因座发现的变异模式表明，拟果蝇X染色体末端最近发生了一次选择性清除，但黑腹果蝇或毛里求斯果蝇没有。将ci和无义基因座的数据与三个经历正常重组水平的X染色体基因座（周期蛋白、玉色和卵黄蛋白2）的数据进行了比较。通过检查估计的系谱以及不同类型突变积累的速率，我们得出结论，选择性清除在第四条染色体上很常见，但在X染色体末端附近则较少见。黑腹果蝇、毛里求斯果蝇和塞舌尔果蝇在ci基因座呈现出有趣的低变异模式，这表明即使在这些物种分化开始后，它们之间可能也发生了一次选择性清除。
