Mutations occur spontaneously, usually during DNA replication. Mutagens are chemical, physical or biological agents that can cause or increase the rate of mutations.
- Ionising radiation such as X-rays can break DNA strands. Mutations may occur during the repair process.
- Deaminating agents can change cytosine to uracil.
- Alkylating agents can attach methyl or ethyl groups to bases leading to incorrect base-pairing.
- Base-analogues may be incorporated or viral DNA may insert itself into the genome.
- Free radicals may oxidise nucleotides and disrupt base-pairing. The loss of a purine or pyrimidine base often occurs spontaneously.
