3.37B understand that the incidence of mutations can be increased by exposure to ionising radiation (for example, gamma rays, x-rays and ultraviolet rays) and some chemical mutagens (for example, chemicals in tobacco)

There are 2 ways in which mutations can occur: Chromosomal mutation and gene mutation.

Chromosomal mutation:
- Caused by a change in number/length/arrangement of chromosomes in the nucleus.
For example, down syndrome is caused by a mutation of an extra copy of chromosome 21, giving them 3 chromosomes instead of 2.
- A chromosomal mutation is often found in tumour cells that can develop cancers.

Different forms of chromosomal mutation:
Duplication: nucleotide inserted twice instead of once, and the entire base sequence is altered.
Deletion: a nucleotide is missed out, and the entire base sequence is altered.
Substitution: different nucleotide is used and may code for a different amino acid. The structure of protein molecule could potentially be different.

Gene mutation:
1. Ionising mutation
Electromagnetic spectrums may cause mutations when in contact with chromosomes in DNA molecules. Gamma rays, x-rays, UV rays are all types of ionising radiation which can damage bonds and cause changes in base sequences.
2. Chemical mutagens
Chemicals like carcinogens and tar in cigarettes can cause mutations.

*Increased rates of mutation cause cells to become cancerous, which is why the above are linked to increased incidence of cancers