如何判别功能基因受到的自然选择？

熊荣川 译

对比同义替换与非同义替换的比率为研究DNA序列进化提供了一种重要的方法。对于自然选择而言，同义突变表型非常不明显，而非同义突变则要受到强大的选择压力。因此，计算两种突变的比率为理解自然选择对分子序列的进化提供了有力的工具。其中一种量度指标就是非同义突变数（dN）与同义突变数（dS）的比率（ω= dN/ dS），它也被MIYATA和YASUNAGA（1980）成为“接受率”。同义突变数/同义突变数（ω= dN/ dS）是一个指示蛋白质水平上选择压力的重要指标：ω=1意味着中性突变，ω＜1表示保守选择，ω＞1则为趋于功能分化的正向选择。

原文：

Codon-Substitution Models for Heterogeneous Selection Pressure at Amino Acid Sites

COMPARISON of synonymous (silent) and nonsynonymous (amino acid-altering) substitution rates provides an important means for studying the mechanisms of DNA sequence evolution (KIMURA 1983; GILLESPIE 1991; OHTA 1993). As synonymous mutations are largely invisible to natural selection (but see AKASHI 1995), while nonsynonymous mutations can be under strong selective pressure, comparison of the fixation rates of these two types of mutations provides a powerful tool for understanding the effect of natural selection on molecular sequence evolution. A measure that has featured prominently in such studies is the nonsynonymous/synonymous substitution rate ratio (ω= dN/ dS), termed the "acceptance rate" by MIYATA and YASUNAGA (1980).

The nonsynonymous/synonymous rate ratio (ω= dN/ dS) is an important indicator of selective pressure at the protein level, withω=1 meaning neutral mutations, ω＜1 purifying selection, and ω＞1 diversifying positive selection.(Yang et al., 2000)

参考文献：

Yang Z, Nielsen R, Goldman N,Pedersen AMK (2000). "Codon-substitution models for heterogeneous selection pressure at amino acid sites." Genetics 155(1): 431.