CHROMOSOMAL PARACENTRIC INVERSIONS IN INTERVARIETAL HYBRIDS OF OAT MAY EXPLAIN ANOMALIES IN MAPPING POPULATIONS

Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada K1A 0C6

Duplicated regions and other anomalies have been suggested by segregation patterns of RFLP markers in hexaploid oat mapping populations. To investigate the cause of this, we examined chromosomes at meiosis in F₁ hybrids from Tibor × Marion, Hinoat × Newman, Marion × Tibor and Hinoat × Marion. A very low frequency of quadrivalent configurations was observed in most plants of most hybrid combinations. A-I bridges were observed at frequencies of 30 - 49% in Hinoat × Newman and 7% in some but not all Tibor × Marion F₁ hybrids. In meiocytes where bridges occurred, single bridges were most common but up to five bridges were seen in some cells. The single A-I bridge configurations were the result of single crossovers or 3 strand double crossovers in the inverted segments in inversion heterozygotes. Double bridges were the result of four strand double crossovers in the inversion loops. The expected free fragments that accompany a bridge configuration were rarely seen at A-I but were frequently present in the cytoplasm of telophase I & II. There was some decline in proportion of stainable pollen in plants containing inversions. The above observations indicate that the cultivars Hinoat and/or Newman and to a lesser extent Terra and/or Marion contain paracentric inversions. Some of the consequences of the presence of inversions include asynapsis and nonhomologous pairing in regions adjacent to the inversion, thus causing reduced recombination in those regions. Chromatids with duplication and deficiencies would result from recombination in the inversion loop leading to the production of gametes with duplications and deficiencies. Such gametes could produce populations showing the observed altered ratios of parental genotypes and lines with duplications of chromosome regions.