Synapsis — the precise pairing of homologous chromosomes along their entire length — occurs during pachytene (the third stage of Prophase I). Prophase I is divided into: leptotene (chromosomes condense), zygotene (synapsis begins), pachytene (synapsis complete, synaptonemal complex fully formed, crossing-over occurs), diplotene (synaptonemal complex dissolves, chiasmata visible), and diakinesis (chromosomes maximally condensed). Pachytene is specifically when the synaptonemal complex is fully assembled.