Crossover

Crossover is the operator actually responsible for the exchange of genetic material between the parents in order to produce their offspring. In the usual case of binary encoding, the simplest crossover operator randomly selects a bit position in the binary string representing an individual (a chromosome), and then two children are produced by taking the bits to the left of the crossover point in parent one and those to the right in parent two and vice-versa. This is called single-point crossover. More than one point may be selected, two, for example, such that one child consists of the bits from the two points to the ends in one parent and those in between the two points from the other parent. The other child will be similarly produced by exchanging the role of the two parents. In the limit a child may be produced by randomly selecting, for each bit, the value from one or the other parent. This is called uniform crossover. It is important to notice that crossover is not necessarily applied to all couples, but only according to a given probability, usually between 0.5 and 0.9. Also, when using other encodings, for example floating-point numbers, the operator must be adjusted Haupt and Haupt (1998).