Aquadro C F, Lado K M, Noon W A
Section of Genetics and Development, Cornell University, Ithaca, New York 14853.
Genetics. 1988 Aug;119(4):875-88. doi: 10.1093/genetics/119.4.875.
A 40-kb region around the rosy and snake loci was analyzed for restriction map variation among 60 lines of Drosophila melanogaster and 30 lines of Drosophila simulans collected together at a single locality in Raleigh, North Carolina. DNA sequence variation in D. simulans was estimated to be 6.3 times greater than in D. melanogaster (heterozygosities per nucleotide of 1.9% vs. 0.3%). This result stands in marked contrast to results of studies of phenotypic variation including proteins (allozymes), morphology and chromosome arrangements which are generally less variable and less geographically differentiated in D. simulans. Intraspecific polymorphism is not distributed uniformly over the 40-kb region. The level of heterozygosity per nucleotide varies more than 12-fold across the region in D. simulans, being highest over the hsc2 gene. Similar, though less extreme, variation in heterozygosity is also observed in D. melanogaster. Average interspecific divergence (corrected for intraspecific polymorphism) averaged 3.8%. The pattern of interspecific divergence over the 40-kb region shows some disparities with the spatial distribution of intraspecific variation, but is generally consistent with selective neutrality predictions: the most polymorphic regions within species are generally the most divergent between species. Sequence-length polymorphism is observed for D. melanogaster to be at levels comparable to other gene regions in this species. In contrast, no sequence length variation was observed among D. simulans chromosomes (limit of resolution approximately 100 bp). These data indicate that transposable elements play at best a minor role in the generation of naturally occurring genetic variation in D. simulans compared to D. melanogaster. We hypothesize that differences in species effective population size are the major determinant of the contrasting levels and patterns of DNA sequence and insertion/deletion variation that we report here and the patterns of allozyme and morphological variation and differentiation reported by other workers for these two species.
在北卡罗来纳州罗利市的一个地点收集了60条黑腹果蝇品系和30条拟果蝇品系，对rosy和snake基因座周围40kb的区域进行了限制性图谱变异分析。据估计，拟果蝇的DNA序列变异比黑腹果蝇大6.3倍（每核苷酸杂合度分别为1.9%和0.3%）。这一结果与包括蛋白质（等位酶）、形态学和染色体排列等表型变异研究的结果形成了显著对比，这些表型变异在拟果蝇中通常变异性较小且地理分化程度较低。种内多态性在40kb区域内分布并不均匀。拟果蝇中每核苷酸的杂合度水平在整个区域内变化超过12倍，在hsc2基因上最高。在黑腹果蝇中也观察到了类似但不太极端的杂合度变化。种间平均分歧度（校正种内多态性后）平均为3.8%。40kb区域内的种间分歧模式与种内变异的空间分布存在一些差异，但总体上与选择中性预测一致：物种内多态性最高的区域通常也是物种间分歧最大的区域。观察到黑腹果蝇的序列长度多态性水平与该物种的其他基因区域相当。相比之下，在拟果蝇染色体之间未观察到序列长度变异（分辨率极限约为100bp）。这些数据表明，与黑腹果蝇相比，转座元件在拟果蝇自然发生的遗传变异产生中所起的作用至多很小。我们推测，物种有效种群大小的差异是我们在此报告的DNA序列和插入/缺失变异的对比水平和模式以及其他研究人员报道的这两个物种的等位酶和形态变异及分化模式的主要决定因素。
