Carcinogens, toxic chemicals, mutagens etc. Many chemical mutagens require biological activation to become mutagenic. Examples of carcinogens that are not mutagens include alcohol and estrogen. Most mutagens are also considered to be carcinogens. The most widely used chemical mutagens are alkylating agents. Early attempts at mutagenesis using radiation or chemical mutagens were non-site-specific, generating random mutations. In vitro, mutations of FR may occur by natural cause or by exposure to mutagens. Random mutations inside the CDRs are introduced using radiation, chemical mutagens or error-prone PCR. Inactivation of caretaker genes is environmentally equivalent to exposing the cell to mutagens incessantly. Mutations come from errors made during the replication of DNA or from exposure to mutagens. DNA damage occurs constantly because of chemicals (e.g. intercalating agents), radiation and other mutagens. Introduction of mutations into an organism may be accomplished by introducing them to mutagens. The rate of mutation may be increased by mutagens. In some organisms mutagens can be useful for performing saturation screens. Efforts to minimize exposure to other known environmental mutagens are also advisable.