Cytological and Cytogenetical Studies on Normal and Interchange Allium Triquetrum
Interchanges (otherwise known as segmental chromosome interchanges or reciprocal translocations), involving exchanges of segments of nonhomologous chromosomes, have been studied extensively in plants. Probably the earliest observations were those of Gates (1903) on a ring of chromosomes at meiosis in Oenothera rubrinervis. Belling's reports of sterility in hybrids amongst certain velvet beans (Stizolobium) were later attributed to an interchange of chromosome segments (Belling, 1925). More clearly defined early cases were provided by McClintock's (1930) cytological demonstrations of interchanges in maize. Burnham's (1956) review indicates a sizable accumulation of data in plants. The researches in maize by Brink, McClintock and Burnham, and others, are by far the most extensive, and these data have contributed much to our present understanding of many cytological processes, particularly synapsis, chiasma formation and orientation phenomena.