Crossing over and meiosis

Crossing over or recombination actually results from exchange of chromosome segments which is believed to take place during prophase I of meiosis. During prophase I of meiosis, homologous chromosomes are brought together during synapsis at zygotene. Each chromosome also divides longitudinally into two chromatids at this stage. At pachytene, chromatids exchange segments. Homologous centromeres then start separating away from one another (terminalization) and figures of chiasmata are theTesult and not the cause of crossing over.