Tetrad analysis with translocation heterozygotes in cranberry (Vaccinium macrocarpon Ait.): Interstitial chiasma and directed segregation of centromeres

Tetrad analysis of translocation heterozygotes was used in cranberry (Vaccinium macrocarpon Ait.) to study the co-orientation of centromeres during meiosis I and its relationship with the frequency of interstitial chiasma. Pollen tetrads from one reciprocal and three cyclical translocation heterozygotes were analyzed and their frequency distribution, as manifest in pollen stainability, was determined. Pollen tetrads were characterized as having four, two, one or zero stained pollen grains. The occurrence of each type was the result of the type of centromere segregation and the presence of crossing over in the interstitial region(s). Based on this information, the predominance of alternate segregation was found to be correlated with a reduction of the crossing over in the interstitial region. Significant differences were found in the tetrad frequency distribution for pollen stainability between years, and for cultivars carrying the same translocation. This variation was correlated with significant differences in the frequency of crossing over between years and among cultivars, which indicates that the estimation of recombination frequencies was influenced by both environment and genotype. The occurrence of translocations in cultivars selected from wild populations indicates the possible advantage of maintaining heterozygosity or a block of genes as a linkat through this chromosome aberration in a self-pollinated crop like cranberry.