The mutation operator is a genetic operator which increases the variability of the population.  Mutation is a random process:  each allele in each chromosome in each individual has a finite probability of changing, called the mutation rate.  For continuous chromosomes, this changing means the simple inversion of a gene’s allele value from 0 to 1 or vice versa.  For an enumerated chromosome, the mutation swaps the values of two different alleles in the chromosome.  In biological systems, the probability of mutation is small.  Though mutation allows minor changes to the population genetics, it prevents the complete degeneration of the population through selection and elimination.  Without mutation, any population degenerates very quickly.