Mutation means a sudden phenotyic change in a character of an individual, not due to crossing or segregation or an alteration in the macro-molecule of DNA(where it remains open, whether the alternation leads to change in gene function or not).It also means the augmentation of genetic material through nucleotide or gene copies, through additional individual chromosomes, as well as through the multiplication of whole genomes towards polyploidy.

Plant breeding requires genetic variation of useful traits for crop improvement. Often, however, desired variation is lacking. Mutagenic agents, such as radiation and certain chemicals, then can be used to induce mutation and generate genetic variations from which desired mutants may be selected. Therefore, mutation breeding means:(1)The phenotypic alternation, and (2)The various underlying molecular and numerical changes. But in any case, a mutation has to be phenotyically expressed to be selectable, all other mutations are only of scientific interest.