Zygotene is the second stage of prophase I during this stage synaptonemal complex formation occur. In pachytene the four chromatids of each bivalent chromosomes becomes distinct and clearly appears as tetrad and in this stage crossing over occurs.
Diplotene is recognised by the dissolution of the synaptonemal complex and the tendency of the recombined homologous chromosomes of the bivalents to separate from each other except at the sites of crossovers. These -shaped are called chiasmata. Diakinesis is marked by terminalisation of chiasmata.

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