Ka，Ks 的概念和意义Ks（synonymous substitutions）：同义替换，即一个密码子中碱基的突变不改变该密码子编码的氨基酸。Ka（nonsynonymous substitutions）：非同义替换，即一个密码子中碱基的突变改变该密码子编码的氨基酸。dN/dS 相当于 Ka/Ks，其意义如下：Neutral Evolution (drift): dN/dS ratio = 1 implies there has been equal numbers of synonymous (dna substitutions that do not affect the protein sequence) and non-synonymous changes (dna substitutions that do affect the protein sequence) during the time between ancestral to the modern versions of the protein.Positive Selection (adaptive evolution): dN/dS ratio > 1 implies there has been more non-synonymous changes than synonymous changes. There has been evolutionary pressure to escape from the ancestral state - i.e. positive selection pressure. This ca
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