The Analysis of Meiosis in Hybrids. Ii. Triploid Hybrids

Abstract

Methods are developed that allow a quantitative determination of relative affinity in triploid hybrids. This results in new insights into the analysis of meiosis in hybrids, genomic relationships and the assignment of genome symbols. The separate recording of open and closed chromosome figures in meiotic analyses is shown to be essential.

Introgression mapping in the grasses. II. Meiotic analysis of the Lolium perenne/Festuca pratensis triploid hybrid

“…Alonso & Kimber (1981) observed that curves showing the relationship of x to the number of ring bivalents and x to the number of trivalents always intersect at an x-value of 0.8. Thus, if the number of trivalents is greater than the number of ring bivalents (x is less than 0.8), then the hybrid can be considered to be a 3:0 type.…”

“…In other hybrids, in which it has not previously been possible to identify the chromosomes from different genomes, the extent to which homoeologous and homologous pairing occurs has been estimated using mathematical models. One such model (Alonso & Kimber, 1981;Chapman & Kimber, 1992) was applied to the present data in order to determine the accuracy of its predictions. This model was chosen as it has been found to show results similar to other mathematical models.…”

“…Generally, a hybrid with a value of x above 0.8 is considered to be a 2:1 type, in which two genomes have an equal affinity with each other and an equal and lower affinity with a third genome. A hybrid with a value of x less than 0.8 is considered to be a 3:0 type, in which all the genomes have an equal affinity (Alonso & Kimber, 1981). Chapman & Kimber (1992) developed the equation shown below to determine the relationship (the relative affinity) between the three genomes in a triploid x = 2 2w<Z6w 2 3 w , where x = the relative affinity and…”

“…Thus, this information allows predictions to be made of the likelihood of transferring specific target genes from one species to another. Genome relationships can be studied by meiotic analysis of polyploid hybrids, and the development of mathematical models has led to a more objective, quantitative approach (Alonso & Kimber, 1981;Crane & Sleper, 1989;Chapman & Kimber, 1992;Sybenga, 1996). Although mathematical models have proved to be invaluable for determining genome relationships, they become redundant if it is possible to distinguish individual genomes and chromosomes in a hybrid either morphologically or using cytological techniques such as C-banding, fluorescent in situ hybridization (FISH) or genomic in situ hybridization (GISH) (Phillips & Strickland, 1966;Naranjo et al, 1987;King et al, 1993King et al, , 1994Miller et al, 1994).…”

Developments in the meiotic analysis of hybrids. III. Amended models for pentaploids

“…The necessary conditions for its application are that the hybrid to be investigated is polyploid to allow the opportunity for preferential pairing, that the cross can be made and the plants brought to flowering, and that the chromosome figures formed at metaphase I of meiosis can be identified. In this series of papers the models for meiotic analysis developed by Alonso & Kimber (1981), Kimber & Alonso (1981) and Espinasse & Kimber (1981) for triploid, tetraploid and pentaploid hybrids, respectively, are being re-examined and extended. Chapman & Kimber (1992a) demonstrated an advantage in weighting meiotic figure frequencies by the number of chromosomes each contains when calculating the merit function to be minimized during optimization.…”