Balakirev Evgeniy S, Ayala Francisco J
Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697-2525, USA.
Genetics. 2003 Dec;165(4):1901-14. doi: 10.1093/genetics/165.4.1901.
We have investigated nucleotide polymorphism in the Est-6 gene region in four samples of Drosophila melanogaster derived from natural populations of East Africa (Zimbabwe), Europe (Spain), North America (California), and South America (Venezuela). There are two divergent sequence types in the North and South American samples, which are not perfectly (North America) or not at all (South America) associated with the Est-6 allozyme variation. Less pronounced or no sequence dimorphism occurs in the European and African samples, respectively. The level of nucleotide diversity is highest in the African sample, lower (and similar to each other) in the samples from Europe and North America, and lowest in the sample from South America. The extent of linkage disequilibrium is low in Africa (1.23% significant associations), but much higher in non-African populations (22.59, 21.45, and 37.68% in Europe, North America, and South America, respectively). Tests of neutrality with recombination are significant in non-African samples but not significant in the African sample. We propose that demographic history (bottleneck and admixture of genetically different populations) is the major factor shaping the nucleotide patterns in the Est-6 gene region. However, positive selection modifies the pattern: balanced selection creates elevated levels of nucleotide variation around functionally important (target) polymorphic sites (RsaI-/RsaI+ in the promoter region and F/S in the coding region) in both African and non-African samples; and directional selection, acting during the geographic expansion phase of D. melanogaster, creates an excess of very similar sequences (RsaI- and S allelic lineages, in the promoter and coding regions, respectively) in the non-African samples.
我们研究了来自东非(津巴布韦)、欧洲(西班牙)、北美(加利福尼亚)和南美(委内瑞拉)自然种群的四个黑腹果蝇样本中酯酶-6(Est-6)基因区域的核苷酸多态性。在北美和南美样本中有两种不同的序列类型,它们与Est-6同工酶变异不完全相关(北美)或完全不相关(南美)。在欧洲和非洲样本中,分别出现不太明显或没有序列二态性的情况。非洲样本中的核苷酸多样性水平最高,欧洲和北美样本中的较低(且彼此相似),南美样本中的最低。非洲的连锁不平衡程度较低(显著关联为1.23%),但在非非洲种群中要高得多(欧洲、北美和南美分别为22.59%、21.45%和37.68%)。有重组情况下的中性检验在非非洲样本中显著,但在非洲样本中不显著。我们认为种群历史(瓶颈效应和遗传上不同种群的混合)是塑造Est-6基因区域核苷酸模式的主要因素。然而,正选择改变了这种模式:平衡选择在非洲和非非洲样本中,在功能重要的(靶标)多态性位点(启动子区域的RsaI-/RsaI+和编码区域的F/S)周围产生了升高的核苷酸变异水平;在黑腹果蝇地理扩张阶段起作用的定向选择,在非非洲样本中产生了大量非常相似的序列(分别在启动子和编码区域的RsaI-和S等位基因谱系)。