Definition

This is where two of selected offspring “breed”. There are two types:

Binary Encoding

In single-point crossover a single crossover point is selected and the two children are formed from the spliced chromosomes of their parents which are both separated and attached at that point

In $k$ point crossover, $k$ crossover points are selected randomly and the the chromosome parts are chosen from either parent with equal probability.

Real Encoding

In averaging crossover, a gene $g$ in the offspring taking values $g_{1}$ and $g_{2}$ in two parents takes the values $$g_{1}\leftarrow\alpha g_{1}+(1-\alpha)g_{2}$$ $$g_{2}\leftarrow(1-\alpha)g_{1}+\alpha g_{2}$$ $\alpha\in[0,1]$