1. Spontaneous mutation: It occurs suddenly and its origin is unknown. It is reported in nature in many cases such as bread mold, microorganism , mice, human, etc.

2. Induced mutation: Mutation can be induced artificially by exposing the organism to abnormal environment such as; radiation, change in temperature, chemicals , etc. They also called mutagens. For e.g;

i) Radiation: X-rays, β-ray, α-ray, u-v light( non-ionizing)

ii) Temperature: Increase in temperature, the increase in rate of reactions and mutation. Sudden change in temperature causes mutagenic effect in the cell.

3. Chemical: Mustard gas, caffeine, hydrogen peroxide, nitro acid, urethane, etc.