Is it farther or further?
1946, from mutation + -gen "thing that produces." Related: Mutagenic; mutagenesis; mutagenize.
mutagen mu·ta·gen (myōō'tə-jən, -jěn')n. An agent, such as ultraviolet light or a radioactive element, that can induce or increase the frequency of mutation in an organism.
Something that causes mutations in living things. Mutagens include chemicals, such as drugs or toxins, and radiation.