What are the Most Important Types of Mutations?

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Mutations can occur both in DNA or RNA.

Mutations can be classified according to the base pair (bp) change at some site.

Types of Mutations


There is no mutation.

Silent Mutation

Only the 3rd base is mutated.

It is less specific.

Silent Mutation

Missense Mutation

In this type of mutation the 2nd base is mutated.

It puts a different amino acid in the protein.

The resulting protein may be functional or non-functional.

Missense Mutation

Nonsense Mutation

This type of mutation also has mutation on the 2nd base. 

It puts a stop codon instead of a different amino acid.

The resulting protein is truncated and non-functional.

Nonsense Mutation

Frameshift Mutation

In this type ONE base is deleted or added.

As a result incorrect amino acid is placed.

May put an early stop codon.

The protein may be truncated and non-functional.

Frameshift Mutation

What If 3 base pairs are added / deleted

If any multiple of 3 added or deleted.

It is NOT a frameshift mutation.

It is simply going to be an insertion or deletion of an AMINO ACID (Codon).

Common Types of Mutations and their Effects

Silent: New Codon Specifies Same Amino acid.


Missense: New Codon Specifies Different Amino acid.

Possible decrease in function; variable effects.

Frameshift / In-frame: Addition or Deletion of Bases.

Usually nonfunctional; Often shorter than normal.

Large Segmental Deletion: (Unequal Crossover in Meiosis).

Loss of function; shorter than normal or entirely missing. α-thalassemia is an example of large segmental deletion.


5’ Splice site (donor) or 3’ Splice site (acceptor).

Variable effects ranging from addition/deletion of a few amino acids to deletion of an entire exon. 

Examples: β-thalassemia, Gaucher’s disease, Tay Sach disease & Lupus.

Triplet Repeat Expansion

Expansion in coding regions cause protein product to be longer than normal and unusable.

Disease often shows anticipation in pedigree.

Huntington’s Disease, Myotonic dystrophy, Fragile X syndrome, Freidreich’s ataxia.

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