a physical or chemical substance that causes permanent hereditary change.
Physical mutagens include ultraviolet radiation and all kinds of ionizing radiation, such as gamma rays, X rays, protons, and neutrons. High and low temperatures are much less capable of causing mutations.
As study intensifies, the list of compounds with mutagenic action grows longer. Among the chemical mutagens are many alkylating compounds, for example, mustard gas, dimethyl sulfate, and nitrosomethylurea; analogs of nitrogenous bases of the nucleic acids, for example, 5-bromouracil and 2-aminopurine; acridine dyes; nitrous acid; some alkaloids; formaldehyde; hydrogen peroxide and some organic peroxides; and some bio-polymers, for example, heterologous DNA and, apparently, heterologous RNA.
The most powerful chemical mutagens, which increase the frequency of mutations hundreds of times, are called super-mutagens. Some viruses might also be considered chemical mutagens, since the mutagenic factor in viruses seems to be located in their DNA or RNA.
Mutagens are apparently universal, that is, they can cause mutations in all forms of life—from viruses and bacteria to the higher plants, animals, and man. Various species differ in their mutability, that is, their sensitivity to mutagens. None of the known mutagens appear to have a lower limit of mutagenic action. However, the frequency of induced mutations decreases with the decreasing dose of mutagen to a point that matches the frequency of spontaneous mutations regularly occurring in the absence of any mutagen.
Physical and chemical mutagens are widely used in breeding agriculturally useful plants and useful microorganisms. Once the mutation is induced, the mutant is artificially removed from the population and bred as a separate species. These mutations are used in artificial selection.