What is the Difference Between Synonymous and Nonsynonymous Mutation

The key difference between synonymous and nonsynonymous mutation is that synonymous mutation is an evolutionary neutral mutation that does not change the amino acid sequence of the protein, while nonsynonymous mutation is an evolutionarily important mutation that changes the amino acid sequence of the protein and undergoes natural selection.

A mutation is a change in the nucleotide sequence of a gene or a genome of an organism. Mutations make changes in the genetic information carried by the genes. This causes changes in the structure of proteins encoded by genes. There are different types of mutations, including point mutation, frame-shift mutation, nonsense mutation and missence mutation. Mutations are the major sources of natural selection and adaptation. Some mutations do not change the expression of the gene and the protein product. They are known as synonymous mutations. Synonymous mutations are evolutionary neutral. Other mutations change the gene and make changes in the resultant protein product. These mutations are known as nonsynonymous mutations. Nonsynonymous mutations undergo natural selection, and they are evolutionary important.

CONTENTS

1. Overview and Key Difference
2. What is Synonymous Mutation
3. What is Nonsynonymous Mutation
4. Similarities – Synonymous and Nonsynonymous Mutation
5. Synonymous vs Nonsynonymous Mutation in Tabular Form
6. Summary – Synonymous vs Nonsynonymous Mutation

What is Synonymous Mutation?

A synonymous mutation is a kind of silent mutation that does not change the amino acid sequence of the protein product. Therefore, synonymous mutations do not change the protein. These mutations are evolutionary neutral, unlike nonsynonymous mutations.

The majority of synonymous mutations are point mutations. Though a single base pair is different in the mutated codon, it gives the same amino acid as the original codon gives. Therefore, the amino acids sequence does not change. When the amino acid sequence is not changed, the protein remains unchanged.

What is Nonsynonymous Mutation?

A nonsynonymous mutation is an alteration of the nucleotide sequence of a gene that changes the amino acid sequence of the protein. Such mutations change the structure and the function of the protein. Hence, these mutations affect individuals, unlike synonymous mutations. Furthermore, nonsynonymous mutations frequently undergo natural selection. Therefore, they are evolutionary important.

There are several types of nonsynonymous mutations; missense mutations and nonsense mutations are two types among them. In nonsynonymous mutations, insertions or deletions often take place. As a result, the entire reading frame changes and the codons become mixed. This causes changes in the resulting amino acid sequence. If the insertion or deletion occurs at the beginning of the nucleotide sequence, the entire amino acid sequence will be changed, producing a completely different protein. Some nonsynonymous mutations bring positive changes that are favourable and are selected from natural selection. Moreover, nonsynonymous mutations increase the diversity in the gene pool.

What are the Similarities Between Synonymous and Nonsynonymous Mutation?

• Synonymous and nosynonymous mutations are two types of mutations that change the nucleotide sequence.
• Point mutations occur in both types.

What is the Difference Between Synonymous and Nonsynonymous Mutation?

Synonymous mutation does not change the amino acid sequence, while nonsynonymous mutation changes the amino acid sequence. So, this is the key difference between synonymous and nonsynonymous mutation. Moreover, synonymous mutations are functionally silent and evolutionary neutral whereas nonsynonymous mutations are evolutionary important. In addition, nonsynonymous mutations are responsible for the increase of the diversity in the gene pool, while synonymous mutations are not.

The below infographic presents the difference between synonymous and nonsynonymous mutation in tabular form for side by side comparison.

Summary – Synonymous vs Nonsynonymous Mutation

Synonymous mutations do not change the amino acid sequence of the protein. They are silent mutations that are evolutionary neutral. Nonsynonymous mutation changes the amino acid sequence of the protein. These types of mutations are frequently subject to natural selection as well since they bring a biological change in the organism. Thus, this is the summary of the difference between synonymous and nonsynonymous mutation.

Reference:

1. “Nonsynonymous Substitution.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “DNA mutation” By Ultrabem – Own work (CC0) via Commons Wikimedia
2. “Frameshift mutation” By Sumukal – Own work (CC BY-SA 3.0) via Commons Wikimedia