Chiasma | The term which Janssens (1909) introduced for the nodes (Gk. chiasma; cross) where the individual chromosomes making up each pair remain in contact during the diplotene and diakinetic stages of prophase 1 and during metaphase 1 of meiosis. It is now established that a chiasma arises as a consequence of crossing-over. In some organisms the chiasmata move towards the ends of the chromosome arms during late diplotene and diakinesis will then no longer correspond to that of the cross-over. The expression 'terminal chiasma' was coined by Newton and Darlington ( 1929) for the end-to-end association of homologous chromosome arms as a result of chiasma movement to the end. |