EVIDENCE FOR ADAPTIVE EVOLUTION OF THE G6PD GENE IN THE DROSOPHILA-MELANOGASTER AND DROSOPHILA-SIMULANS LINEAGES
EVIDENCE FOR ADAPTIVE EVOLUTION OF THE G6PD GENE IN THE DROSOPHILA-MELANOGASTER AND DROSOPHILA-SIMULANS LINEAGES
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DOI：
10.1073/pnas.90.16.7475
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发表时间：
1993-08-15
影响因子：
11.1
通讯作者：
YOON, J
中科院分区：
文献类型：
--
作者：
EANES, WF;KIRCHNER, M;YOON, J
中性理论的支持者认为，分子水平的进化主要反映了中性突变的随机遗传漂变过程。根据这一理论，种间差异和种内多态性的水平，预计将相关的核苷酸或氨基酸序列的类别与不同程度的功能限制，如同义和替换位点。多态性降低的核苷酸位点应显示种间差异显著降低的水平。为了验证这一假设，我们分别对黑腹果蝇和拟果蝇的葡萄糖-6-磷酸脱氢酶（G6 PD）基因的32个和12个拷贝进行了测序。这两个物种在同义位点表现出相似的核苷酸多态性水平。D.黑腹果蝇显示两种氨基酸多态性，一种与世界性等位酶多态性相关，另一种与欧洲和北非人群特有的等位酶多态性相关。与此相反，D. simulans显示没有替换多态性。虽然物种之间的同义分歧为10%，这是其他基因的典型差异，但有21个替换差异。与氨基酸多态性、沉默多态性和分歧水平相比，这种氨基酸序列分歧水平是分子进化中性模型下预期的10倍。我们认为，这种过度的分歧反映了G6 PD上的自然选择事件，导致这两个最近分离的谱系中有利的氨基酸突变的固定。
Proponents of the neutral theory argue that evolution at the molecular level largely reflects a process of random genetic drift of neutral mutations. Under this theory, levels of interspecific divergence and intraspecific polymorphism are expected to be correlated across classes of nucleotide or amino acid sequences with different degrees of functional constraint, such as synonymous and replacement sites. Nucleotide sites with reduced polymorphism should show comparably reduced levels of interspecific divergence. To examine this hypothesis, we have sequenced 32 and 12 copies of the glucose-6-phosphate dehydrogenase (G6pd) gene in Drosophila melanogaster and Drosophila simulans, respectively. Both species exhibit similar levels of nucleotide polymorphism at synonymous sites. D. melanogaster shows two amino acid polymorphisms, one associated with the cosmopolitan allozyme polymorphism and a second with an allozyme polymorphism endemic to European and North African populations. In contrast, D. simulans shows no replacement polymorphism. While synonymous divergence between species is 10%, which is typical of other genes, there are 21 replacement differences. This level of amino acid sequence divergence, when contrasted with levels of amino acid polymorphism, silent polymorphism, and divergence, is in 10-fold excess over that expected under the neutral model of molecular evolution. We propose that this excess divergence reflects episodes of natural selection on G6pd resulting in fixation of advantageous amino acid mutations in these two recently separated lineages.