Crossing over is a biological process in which homologous chromosomes exchange segments of genetic material during meiosis. This exchange of genetic information contributes to genetic diversity in the resulting gametes (sperm and eggs).
Crossing over occurs during prophase I of meiosis. During this phase, homologous chromosomes pair up in a process called synapsis, forming structures known as tetrads. The physical exchange of segments happens at points called chiasmata. This recombination results in chromosomes that carry a mix of genetic information from both parents, which increases genetic variation among the offspring.