Frameshift Mutation — Definition & Examples

What Is a "Frameshift"?

A frameshift mutation results from the insertion or deletion of one or more bases. Since bases are read in groups of three, the addition or deletion of these bases will cause a shift in the "reading frame" and cause the bases to be read wrong. This could have a huge effect on the resulting protein.

Inserting or deleting a multiple of three bases in a genome will not shift the reading frame since bases are read in groups of three.

What Are Frameshift Mutations?

During translation, ribosomes read mRNA sequences and convert them into proteins. They do this by reading groups of three RNA nucleotides. These groups of nucleotides are called codons, and each codon codes for an amino acid.

Chains of amino acids become a protein. In order for a ribosome to produce the correct protein it must read the codons in the correct order. The order that the ribosome reads the nucleotides in is called its reading frame.

What Is an Example of a Frameshift Mutation?

If the sentence below is an mRNA sequence, this is how a ribosome would read it to produce a functioning protein:

the/cat/hat/did/not/fly

However, if even a single letter is deleted or inserted into this sequence, it will ruin the reading frame and the sentence (or protein) will no longer be the same.

tec/ath/atd/idn/otf/ly (deletion of h in the first frame) the/fca/tha/tdi/dno/tfl/y (insertion of f before "cat")

These types of mutations are extremely negative because they can completely destroy the function of the encoded protein. Most proteins can still function if only one amino acid is changed, but a mutation with a frameshift usually produces non-functioning proteins. This is because they can create an early stop codon, causing premature termination, or create a different protein entirely.

Why Do Frameshifts Happen?

These mutations occur when there is either an insertion or a deletion mutation. By inserting or deleting a single nucleotide from the RNA or DNA sequence, the groups of three nucleotides that the ribosomes read get messed up.

This type of mutation only occurs when the number of changes is not a multiple of three. Because the reading frame is in groups of three, if three nucleotides get inserted or deleted, it does not alter the reading frame. However, this could still lead to another type of mutation, including a silent, missense, or nonsense mutation.

$$\color{#8925AE}{\text{Vocabulary Review:}}$$

$\color{#8925AE}{\text{Mutation}}$ : A change in genetic code

$\color{#8925AE}{\text{Point Mutation}}$ : A mutation that occurs at a single point in the nucleotide sequence

$\color{#8925AE}{\text{Frameshift}}$ : A mutation that causes all the nucleobases following it to be shifted

$\color{#8925AE}{\text{Codon}}$ : A group of three nucleobases that codes for a specific amino acid

(Video) Frameshift Mutations

by Patrick Haney

Frameshift mutations occur when a base pair is added or deleted from the genetic information. This type of mutation changes the way that codons are read and results in a change in the final amino acid sequence. A change like this can damage the final protein's structure and ability to function correctly.