Origin of Mutagenesis

Mutations mainly originate from limited fidelity of DNA replication and DNA damage. Additionally, nonhomologous end joining (NHEJ) during repair of doublestrand breaks also leads to mutagenesis. 

Double-strand break is an important class of DNA damage. In cells, doublestrand breaks are repaired by recombination. Whereas homologous recombination is mostly accurate, NHEJ is highly error-prone. Therefore, repair of double-strand breaks by NHEJ frequently results in mutagenesis at sites of DNA joining. 

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