How do synonymous and nonsynonymous DNA mutations differ?

Expert Solution

A mutation is a heritable genetic change in the DNA sequence which results in alternate forms of gene and gene products.

Synonymous Mutations(Ks) : Mutations/substitution or alteration of base pairs in a DNA sequence which result in the formation of new codon which specify the same amino acid as that by the wild type, causing no effect on coding of genome. For eg. GCC--->GCG, both codons code Alanine.

Synonyms mutations are are evolutionary neutral therefore are not subjected to natural selection.

Synonyms mutations are functionally silent because no change in the protein structure coded by the genome occurs retaining the function of the wild type protein.

Non synonymous Mutations (Ka): A mutation resulting in altered amino acid sequence, which codes a different amino acid from that of wild type sequence is known as Non synonymous mutation. For eg. CCA--->CAA result in formation of glutamine instead of Proline which is coded by the wild type sequence, hence result in the altered protein structure.

Natural selection applies frequently on nonsynonymous mutations.

Ratios of synonyms to nonsynonymous mutations are used for estimation of selection pressure which is applied on a protein whose sequence has been subjected to mutation. For eg. Ka/ks =1(neutral selection), Ka/Ks<1 (purifying selection), Ka/Ks>1(Positive selection).

gladiator answered 2 years ago

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