A gene mutation is a change in the DNA base sequence.

Most gene mutations happen spontaneously during the process of DNA replication.

Mutagens are factors that increase the rate of mutations such as ultraviolet and ionising radiation, chemicals and viruses.

A substitution mutation is when one base is replaced by another.

A deletion mutation is when one base is removed from the DNA sequence.

An insertion mutation is when one base is added into the DNA sequence.

Many substitution mutations have no effect on protein structure because the genetic code is degenerate. This means that substitutions often result in the same amino acid being coded for.

Deletion mutations are likely to change protein structure because they cause a frameshift to the left  which changes the amino acid sequence.

A frameshift is when the entire sequence after a mutation is shifted either to the left or the right.

Insertion mutations are likely to affect protein structure because they cause a frameshift to the right  which changes the amino acid sequence.