Developments in the meiotic analysis of hybrids. I. Review of theory and optimization in triploids

Abstract

The theory, construction and optimization of a model of chromosome pairing in triploid hybrids are re-examined and the model reconstructed. A new approach to optimization is described that removes a bias in the estimation of x, the measure of relative affinity, by weighting the observed and calculated meiotic figure frequencies by the number of chrOmosomes in each figure type. The amended analysis is compared with its antecedent and with other models.

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

“…Both are equally and more distantly related to genome 3 with a relative affinity of y so that x y. The relative affinity is expressed as the proportions of the three different arm pairings that may be formed so that the ratio among (1-2) (1-3) and (2-3) arm pairs is x : y : y (Chapman & Kimber, 1992). The values of x and y will therefore be related by the equation xǹy = 1.…”

“…However, in the LpLpFp hybrid, there were significantly more frying pan trivalents (137) than linear or V-shaped trivalents (99) ( 2 1 = 5.8, P 0.02). Chapman & Kimber (1992) warn that, should a data set include a high frequency of complex figures (frying pan, 'bird cage' and triradial trivalents), it is generally unanalysable using their model. The high frequency of frying pan trivalents in our data shows that there is more than one pairing initiation site per chromosome arm.…”

“…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…”

“…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.…”

“…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).…”