Contrasting the efficacy of selection on the X and autosomes in Drosophila.
Contrasting the efficacy of selection on the X and autosomes in Drosophila.
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DOI：
10.1093/molbev/msm275
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发表时间：
2008-02
影响因子：
10.7
通讯作者：
Nadia D Singh;A. Larracuente;A. Clark
中科院分区：
文献类型：
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作者：
Nadia D Singh;A. Larracuente;A. Clark
为了研究正向自然选择和纯化自然选择对果蝇X染色体和常染色体的相对有效性，我们利用12个物种的新获得的同源基因比对，比较了这些染色体组之间的分子进化速率和模式。可能影响相对X对常染色体替换率的参数包括相对有效种群大小、男性和女性生殖系突变率、等位基因对适应度的影响分布以及新突变的显性程度。我们的分析表明，对于X连锁基因，密码子的使用偏差一直更大，这表明净化选择在X染色体上的效果一直比在果蝇系统发育中的常染色体上更大。然而，我们的结果与正选择的有效性不太一致，只有一些谱系在X染色体上显示出较高的替换率。这表明，突变的选择效应的分布或其他相关参数在不同物种之间具有足够的可变性，从而以不同的方式在个体谱系中扭转平衡。这些数据表明，替代率不仅仅是由适应性进化决定的。这一全基因组分析提供了一幅清晰的图景，表明选择的效果在基因内是不同的，而且在净化选择的情况下，这种效果在整个系统发展史中明显更加一致。我们的结果还表明，只有当驱动替换率的相关种群遗传参数在物种和染色体环境中不同时，预测X和常染色体之间进化速度系统差异的简单模型才能与这些果蝇数据兼容。
To investigate the relative efficacy of both positive and purifying natural selection on the X chromosome and the autosomes in Drosophila, we compared rates and patterns of molecular evolution between these chromosome sets using the newly available alignments of orthologous genes from 12 species. Parameters that may influence the relative X versus autosomal substitution rates include the relative effective population sizes, the male and female germline mutation rates, the distribution of allelic effects on fitness, and the degree of dominance of novel mutations. Our analysis reveals that codon usage bias is consistently greater for X-linked genes, suggesting that purifying selection consistently has greater efficacy on the X chromosome than on the autosomes across the Drosophila phylogeny. However, our results are less consistent with respect to the efficacy of positive selection, with only some lineages showing a higher substitution rate on the X chromosome. This suggests that either the distribution of selective effects of mutations or other relevant parameters are sufficiently variable across species to tip the balance in different ways in individual lineages. These data suggest that rates of substitution are not solely governed by adaptive evolution. This genome-wide analysis provides a clear picture that the efficacy of selection varies intragenomically and that this effect is markedly more consistent across the phylogeny in the case of purifying selection. Our results also suggest that simple models that predict systematic differences in rates of evolution between the X and the autosomes can only be made to be compatible with these Drosophila data if the relevant population genetic parameters that drive substitution rates differ among species and chromosomal contexts.