The natural incidence of mutations is increased by mutagens. Mutations may be concentrated at hotspots. A type of hotspot responsible for some point mutations is caused by deamination of the modified base 5-methylcytosine.
Forward mutations occur at a rate of ~10-6 per occur per generation; back mutations are rarer. Not all mutations have an effect on the phenotype.
Epigenetic changes consist of events that change the state or structure of a gene without altering the sequence of base pairs. One example of such a change is the addition of a methyl group to cytosine to generate 5-methylcytosine.
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