The pairing of homologous chromosomes during zygotene is called synapsis i.e., the homologous chromosomes which come from mother and father paired in zygotene. The synsaptonemal complex is also formed. The synaptonemal pair at the pachytene is commonly refered to as bivalents or dyads because it consists of two visible chromosomes or as tetrad because of four visible chromatids. The chromosomes at leptotene become more uncoiled and assume a long thread like shape. The centriole duplicate arid each daughter centriole migrates towards opposite pole. Diplotene is characterised by unpairing of homologous chromosomes. The synaptonemal complex appears to be dissolved leaving physicaly jointed discrete points called chiasmata. On these points crossing over took place.