In this manner, highly fit vectors are allowed to breed, with the hope that they will produce ever more fit offspring. Although the crossover operation may take many forms, it typically involves splitting each parent chromosome at a randomly-selected point within the interior of the chromosome, and rearranging the fragments so as to produce offspring of the same size as the parents. The children usually differ from each other, and are usually different from the parents. The effect of crossover is to build upon the success of the past, yet still explore new areas of the search space. The next operation is mutation, in which individuals are slightly changed.
Mutation is an asexual operation, and usually plays a relatively minor role in the population.
The idea behind mutation is to restore genetic diversity lost during the application of reproduction and crossover, both of which place relentless pressure on the population to converge. The relentless pressure towards convergence is driven by fitness, and offers a convenient termination criteria. In fact, after many generations of evolution via the repeated application of reproduction, crossover, and mutation, the individuals in the population will often begin to look alike, so to speak. At this point, the GA typically terminates because additional evolution will produce little improvement in fitness. Many termination criteria may be used, in which the most simple is to just stop after some predetermined number of generations.