Question

“Synonymous and nonsynonymous” sites essay question

Explain why synonymous sites typically evolve faster than nonsynonymous sites.

Answer 1

A mutation that replaces an amino acid with a similar amino acid is known as a synonymous mutation.

Ex: Leu is replaced with Ile

A mutation that replaces an amino acid with a non-similar amino acid is known as a non-synonymous mutation.

Ex: Leu is replaced with Lys

Synonymous mutations in the coding sequences do not alter the protein function. This is due to the fact that the replaced amino acid also displays similar properties as that of the original amino acid. So, there is no evolutionary constraint on synonymous mutations.

On the other hand, non-synonymous mutations negatively affect protein function. this is due to the fact that the replaced amino acid displays different properties than the original amino acid. So, these mutations can be deleterious. Hence there will be an evolutionary constraint on such mutations.

Synonymous mutations are not under selection pressure. Due to the absence of evolutionary constraint, synonymous mutations evolve faster than non-synonymous mutations.