Ka/Ks Ratio
In genetics, the Ka/Ks ratio (or ω, dN/dS), is the ratio of the number of non-synonymous substitutions per non-synonymous site (Ka) to the number of synonymous substitutions per synonymous site (Ks), which can be used as an indicator of selective pressure acting on a protein-coding gene. Comparisons of homologous genes with a high Ka/Ks ratio are usually said to be evolving under positive selection. The terms Ka/Ks and dN/dS are used interchangeably. Note however that Dn and Ds are different parameters from dN and dS (or KA and KS ). Dn and Ds are count estimates, which represent the total numbers of non-synonymous and synonymous substitutions.
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