Definition for Mutagen
From Biology Forums Dictionary
An agent known to cause mutation.
Mutations can be spontaneous, or result from recombination. Physical or chemical agents called mutagens, which include radiation and several types of DNA-altering chemicals, induce mutations. Radiation in the form of X rays and gamma rays can cause mutations. Additionally, nonionizing radiation in the form of ultraviolet light causes adjacent pyrimidine bases to bond to one another to form pyrimidine dimers. The presence of dimers prevents hydrogen bonding with the nucleotides in the complementary strand, distorts the sugar-phosphate backbone, and prevents proper replication and transcription.
Chemical mutagens include nucleotide analogs, compounds that are structurally similar to normal nucleotides but, when incorporated into DNA, cause mutations. Some nucleotide-altering chemicals alter the structure of nucleotides, causing base-pair substitution mutations. Aflatoxins are nucleotide-altering chemicals that result in missense mutations and cancer. Still other mutagenic chemicals insert or delete nucleotide base pairs, resulting in frameshift mutations.