- Mutagens are chemical, biological or physical agents (things) that cause mutations by changing genes or chromosomes of an organism.
- eg chemicals - pollutants like metal ions (arsenic, cadmium), benzene, preservatives. Biological bacteria and virus, radiation like X-ray or U.V.
Gene (point) mutations
- Change single bases in DNA. There are two main types:
- Base substitution replaces one base with another. If the amino acid is not changed it is a silent mutation. This is a result of redundancy within the genetic code. eg CAC to CAG the amino acid will still be valine. If the amino acid is changed, eg GAC glutamic acid changed to GAA aspartic acid, and the shape of the protein is affected, it can result in a non-functional protein. The change results in a different protein which changes the genotype of the cell eg Bb becomes Bbn (where bn is the new allele with the mutation).
- Frameshift mutation occur when the base is added or deleted from DNA. This changes which bases are read as triplets. This can cause major changes in the protein produced.
- If the mutation occurs in gamete (sex) cells, cells of offspring will carry mutation.