For pole balancing, individuals whose fitness is below average are replaced by reproduction of above average chromosomes. The strategy must be modified if two few or two many chromosomes survive. Operators that recombine the selected chromosomes are called genetic operators. Two common operators are crossover and mutation . Crossover exchanges portions of a pair of chromosomes at a randomly chosen point called the crossover point.
Some Implementations have more than one crossover point.
Offspring produced by crossover cannot contain information that is not already in the population, so an additional operator, mutation, is required. Mutation generates an offspring by randomly changing the values of genes at one or more gene positions of a selected chromosome. The number of offspring produced for each new generation depends on how members are introduced so as to maintain a fixed population size. In a pure replacement strategy, the whole population is replaced by a new one. In an elitist strategy, a proportion of the population survives to the next generation.