A heritable change in the nucleotide sequence of genomic DNA (or RNA in RNA viruses), or in the number of genes or chromosomes in a cell, which may occur spontaneously or be brought about by chemical mutagens or by radiation (induced mutation).
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 161 (https://doi.org/10.1351/pac199264010143)