pachytene /pak″itēn/ [Gk, pachy + tainia, ribbon] , the third stage in the first meiotic prophase of gametogenesis, in which the paired homologous chromosomes form tetrads. The bivalent pairs become short and thick and intertwine so that four chromatids are visible. See also diakinesis, diplotene, leptotene, zygotene.
