Biology 1002B Lecture Notes - Lecture 23: Synonymous Substitution, Molecular Clock, Molecular Evolution
27 Jan 2020
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Synonymous substitution is not changing the protein, doesn"t change the phenotype, they are silent or neutral. Non-synonymous substitutions do affect the protein sequence, can be advantageous or deleterious (more common: characteristics of the neutral theory of molecular evolution. Selection theory suggested every mutation affected fitness, most were deleterious, some were advantageous because there are more ways to screw up an enzyme than make it better. Protein sequencing revealed that lots of the substitutions are not affecting the protein sequence i. e. they are neutral. A smaller fraction of mutations are advantageous: relationship between frequency of amino acid substitutions in given proteins vs. time since common ancestor. If the neutral theory is correct then number of neutral mutations should be proportional to the time since the divergence of two species. The rate of mutations is constant over evolutionary time, this reflects that most mutations are neutral: relative rates of accumulation of synonymous vs. non-synonymous mutations.
