i) The pairing of homologous chromosomes is called synapsis. This occurs during the second stage of prophase I or zygotene. (ii) Bivalent or tetrad is a pair of synapsed homologous chromosomes. They are formed during the zygotene stage of prophase I of meiosis. Bivalent (iii) Chiasmata is the site where two non-sister chromatids of homologous chromosomes have crossed over. It represents the site of cross-over. It is formed during the diplotene stage of prophase I of meiosis. Chiasmata