Mutagenesis is the formation of mutations in DNA molecules. There are a variety of mutations that can occur in DNA, such as changes in the DNA sequence or rearrangement of the chromosomes. Such mutations may occur spontaneously, as a result of 'mistakes' that occur during DNA replication or mitosis. Spontaneous mutations are essential to produce genetic variation necessary for natural selection. Mutations may also occur as a result of environmental exposure to genotoxins (chemicals that alter the structure of DNA). Mutagenesis is of concern because it may lead to irreversible effects that can affect fitness of organisms, which in turn may affect populationlevel processes.
There are potentially thousands of mutagenic and genotoxic agents to which organisms are exposed. Examples of the classes of mutagenic compounds, the DNA damage they elicit, and their sources in the environment are listed in Table 1. Each genotoxin may elicit many different types of DNA damage.
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