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 (Vacci nium macrocarpon Ait.) to study the co-orientation of centromeres during me iosis I and its relationship with the frequency of interstitial chiasma. Po llen tetrads from one reciprocal and three cyclical translocation heterozyg otes were analyzed and their frequency distribution, as manifest in pollen stainability, was determined. Pollen tetrads were characterized as having f our, two, one or zero stained pollen grains. The occurrence of each type wa s the result of the type of centromere segregation and the presence of cros sing over in the interstitial region(s). Based on this information, the pre dominance of alternate segregation was found to be correlated with a reduct ion of the crossing over in the interstitial region. Significant difference s were found in the tetrad frequency distribution for pollen stainability b etween years, and for cultivars carrying the same translocation. This varia tion was correlated with significant differences in the frequency of crossi ng over between years and among cultivars, which indicates that the estimat ion of recombination frequencies was influenced by both environment and gen otype. The occurrence of translocations in cultivars selected from wild pop ulations indicates the possible advantage of maintaining heterozygosity or a block of genes as a linkat through this chromosome aberration in a self-p ollinated crop like cranberry.