mutation of genetic algorithm

Mutation:
In GAs, mutation plays the role of a background operator which arbitrarily inverts one or more bits of a parent chromosome to increase the structural variability of the population. Mutation provides a means to restore lost or unexplored genetic material and prevent the GA from premature convergence to sub-optimal solutions. In this sense, mutation performs an exploration of the search space. Each bit of every chromosome in the population might become subject to an alteration according to a probability denned by a mutation rate Pm. The mutation probability per bit is usually small, typical values for Pm lie in the interval [0.001,0.02]. Therefore, the mutated chromosome is usually very similar to its parents.
1M mutation:

Single gene (chromosome or even individual) is randomly selected
to be mutated and its value is changed depending on the encoding type
used
2- 2M mutation:

Multi genes (chromosomes or even individuals) are randomly selected to be mutated and there values are changed depending on the encoding type used