A model of meiotic chromosome association in triploids

Abstract

A model was developed for chromosome association at meiotic metaphase I in triploids. Probabilities were estimated for each pachytene configuration and for subsequent formation of at least one chiasma in each combination of chromosome arms. Long and short arms were allowed to differ, but were related through an effective arm ratio so that the pattern of genomic affinity was the same for both arms. No other a priori assumptions were made about the pattern of genomic affinity. However, the usual assumptions of genome analysis were made including the following: identity of genomic-affinity pattern and chiasma frequency across homeologous groups, freedom from translocation heterozygosity, independence of chromosome arms, and absence of chiasma formation on both sides of a synaptic partner exchange within an arm. The model was statistically overparameterized and, therefore, had multiple solutions that yielded the same expected meiotic analysis. The range of these solutions can be found through repeated optimizations from randomly chosen starting values within the permitted ranges of the variables. It was convenient to express the optimized pattern of genomic affinity in terms of the proportions of metaphase I association due to each pairwise combination of genomes. Genomic affinity was analyzed in 16 triploid hybrids with the aid of the model.Key words: polyploidy, genome analysis, meiotic model.