A mutation is a change in the DNA of an organism, which is genetically transmitted, and may give rise to a heritable variation. Mutagens, substances that have the competence to produce a mutation, may be subject to chromosomal changes such as deletions, translocations, or inversions. Mutations may also be more subtle, resulting in changes of only one or a few nucleotides in the sequence of DNA. These more subtle mutations are called as "point mutations," and it is these that most people refer to when discussing mutation.

Ordinarily, mutation is thought of as a genetic change that results in alterations in a subsequent generation. Germinal tissue, which gives rise to spermatozoa and ova, is the tissue in which such mutations occur. However, mutations can arise in many cell types in addition to the germ line, and these changes to non-germinal DNA are referred to as somatic mutations. Although...