DNA ass genetic material is relatively stable. However, under many physiological conditions it may also undergo some changes. A mutation is a permanent change in the DNA sequence of a gene. Mutations in a gene's DNA sequence can alter the amino acid sequence and therefore affect the function of the gene product. Mutation can occur at either DNA or chromosome level, spontaneously or induced.
DNA mutation types
DNA mutation includes several types according to its consequence: base pair substitution (transversion or transition); missense mutation, nonsense mutation, neutral mutation, silent mutation and frame-shift mutation.
Cause of mutation
Mutation can be spontaneous, due to the replication errors and/or chemical reactions in cells (such as depurination and deamination). DNA mutation can also be induced by radiation and chemical mutagens.
DNA repair mechanisms
Overall there are two classed of DNA repair mechanisms: direct repair of lesion and repair involving excision of base pairs (BER). Direct repair includes DNA polymerase proofreading, light repair of thymidine dimers, and repair of alkylatiion damage. BER includes excision repair, glycosylase repair, mismatch repair and SOS response.