Quantitative analysis of meiotic chromosome pairing in triploid blueberry: evidence for preferential pairing

Abstract

Mathematical models have been developed to predict meiotic configuration frequency distributions for autoploid (random chromosome pairing) or preferential chromosome pairing behavior. Meiotic chromosome pairing was quantitatively analysed, relative to these models, in six highbush blueberry (Vaccinium corymbosum) triploid (2n = 3x = 36) hybrids derived from three unrelated 4x × 2x crosses. Mean trivalent per cell frequencies ranged from 3.59 to 7.89. Excess univalents were observed in triploids of one cross and are probably a result of disturbance in chiasma formation or maintenance and (or) random pairing failure. Arm chiasmate association values (a and b) ranged from 0.72 to 1.00, with the greatest difference in arm values being 0.18. Trivalent to ring bivalent (r) ratios ranged from 0.59 to 2.02. The observed configuration frequency distributions of three triploids having r-values greater than 1 did not deviate significantly from the autoploid pairing (p = 0) model frequency distribution. Frequency distributions of three triploids having r-values less than 1 deviated significantly from the autoploid model. Ranges for pairing affinity relationships include the possibility of two genomes pairing preferentially at a frequency of 77.7% (0.444 points over the random frequency of 0.333), which suggests the presence of genome divergence in blueberry. However, violation of model assumptions could seriously bias preferential pairing estimates. Segregating genetic factors also appear to be of significance in chromosome pairing behavior.Key words: autotriploids, chromosome pairing, preferential pairing, genome divergence, meiotic configurations.