Chiasmata of bivalents are completely lost due to 

In Anaphase I, due to movement of homologous chromosomes towards opposite poles the terminal chiasmata present at telomeres are completely lost and the chromosomes are drawn towards its respective poles. Synapsis takes place in zygotene during which chiasmata are not formed. Crossing over takes place in pachytene which results in the formation of chiasmata. Terminalisation occurs in diakinesis and it makes the decrease in number of chiasmata.