Cytogenetic Analyses of Autopolyploids: Models and Methods for Triploids to Octoploids

Abstract

Methods are presented for determining the frequencies and numbers of various meiotic configurations expected in autopolyploids. This allows one to test polyploids of unknown origin for agreement with expected meiotic configurations. Rejection of the autoploid hypothesis may indicate the presence of Ph‐like genes or some type of alloploid. The models consider mean chiasma frequencies of 2, 3, and 4 per bivalent for triploids and tetraploids and 2 per bivalent for pentaploids, hexaploids, heptaploids, and octoploids. Literature data for a known autotriploid, autotetraploids, allotetraploids, and allopentaploids were tested against expectations of the models. There was generally good agreement between number of observed autoploid meiotic configuration and those expected in the models.

Meiotic pairing in autohexaploid Lathyrus: a mathematical model

“…Comparison of the observed meiotic metaphase I configuration frequencies with those predicted by the model of Jackson & Casey (1982), although not contradicting this conclusion, showed large differences. That model is based on a frequency of hexavalent pairing of 8/15, a frequency 1995 The Genetical Society of Great Britain.…”

“…The set constructed for pentaploids by Espinasse & Kimber (1981) and an amended version by Chapman & Kimber (1992) are close to what is needed for hexaploids. In these models, like in that of Jackson & Casey (1982), the average arm association frequency c is used, and is considered to be a measure of overall pairing affinity. It is combined with a factor x, measuring relative affinity between the most related two genomes in a polyploid hybrid, and vatying between 0.5 and 1.…”

“…If c is high and x = 0.5, the conclusion is that the plant concerned is an autopolyploid. The assumptions on which these models are based are not identical to those of Jackson & Casey (1982) and the model presented here. The limitations and relative merits of such models have been discussed by Sybenga (1992Sybenga ( , 1995.…”

Meiosis in autopolyploid Crepis capillaris. III. Comparison of triploids and tetraploids; evidence for non independence of autonomous pairing sites

“…Thus in the absence of any pairing preferences among homologues and assuming independence of pairing partner choice at two APSs, the probability of a single PPS is 2/3 (66.6 per cent) for both autotriploids and autotetraploids (Jackson & Casey, 1982;Sybenga, 1975). An additional APS will, on average, generate 2/3 PPS irrespective of whether the trisome or tetrasome already contains one PPS.…”

“…In autopolyploids and polysomics, meiotic pairing is generally restricted to pairwise associations but the chromosomes are able to engage different pairing partners at different regions, thus leading to pairing partner switches (PPSs) and multivalents at prophase I (reviewed by Sybenga, 1975; Gillies, 1989). Many cytologists from Newton & Darlington (1929) onwards have recognized that the special situation in autopolyploids may give unique insights into the organization of pairing, especially as regards the numbers of pairing sites (Klingstedt, 1937;Sved, 1966;Jackson & Casey, 1982). Further consideration of the situation in autopolyploids has resulted in the concept of the autonomous pairing site (APS) as one which is capable of initiating pairing between any two of three or more homologous chromosomes and therefore of generating a PPS but without specifying the probability that this will occur (Callow & Gladwell, 1984).…”