Mutations are changes to the base sequence of DNA

Any change to the base (nucleotide) sequence of DNA is called a mutation.
Mutations can be caused by errors during DNA replication.
The rate of mutation can be increased by mutagenic agents.
The types of mutations that can occur include:

Substitution - one or more bases are swapped for another, e.g. ATGCCT becomes ATTCCT
Deletion - one or more bases are removed, e.g. ATGCCT becomes ATCCT
Addition - one or more bases are added, e.g. ATGCCT becomes ATGACCT
Duplication - one or more bases are repeated, e.g. ATGCCT becomes ATGCCCCT
Inversion - a sequence of bases is reversed, e.g. ATGCCT becomes ACCGTT
Translocation - a sequences of bases is moved from one location in the genome to another. This could be movement within the same chromosome or movement to a different chromosome.

The order of DNA bases in a gene determines the sequence of amino acids in a particular polypeptide.
If a mutation occurs in a gene, the sequence of amino acids in the polypeptides that it codes for could be changed.
Polypeptides make up proteins. A change in the amino acid sequence of a polypeptide may change the final 3D shape of the protein, which could mean that it doesn't work properly.
Some mutations can cause genetic disorders - inherited disorders caused by abnormal genes or chromosomes. Some mutations can increase the likelihood of developing certain cancers.

If a gamete containing a mutation for a genetic disorder or a type of cancer is fertilised, the mutation will be present in the new fetus formed - these are hereditary mutations.

	Created by Lucy Nove over 7 years ago

A2 Biology (Mutations and Gene Expression) Note on Mutations, created by Lucy Nove on 25/01/2017.