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a hereditarily altered form of an organism that differs from the original type in some abnormality that arose through mutation.
Organisms with hereditary changes that appear suddenly have been known for several hundreds of years. For example, at the end of the 18th century a mutant form of sheep with short legs appeared. It later became the first of the Ancona breed. After the discovery of artificial mutagenesis in the 1920’s and 1930’s, numerous mutants of microorganisms, plants, and animals were obtained and used both for actual breeding purposes and for experiments designed to determine patterns in the mutation process. Both the biochemistry of genetics and many metabolic processes were elucidated by means of biochemical mutants that had lost the capacity of the original, wild type microorganism to synthesize essential compounds, such as vitamins, amino acids, and nitrogenous bases.
S. M. GERSHENZON