Meiotic crossing over occurs during gametogenesis when homologous chromosomes pair up and exchange genetic material. The major steps are synapsis, duplication, crossing over, and terminalization. Crossing over involves the physical exchange of non-sister chromatid segments between homologous chromosomes after synapsis, resulting in genetic recombination. There are three types of crossing over: single, where one chromatid is involved; double, where two chromatids are involved; and multiple, where more than two chiasmata are formed, though multiple crossing over is rare.