Abstract
Genetic segregations of a marker locus responsible for red hypocotyl-color (R) and five independently-inherited enzyme-coding loci (Got-2. Lap. Gdh-2, Aph-1, Px-2) in the backcrossed progeny between B. vulgaris or B. maritima and B. macrocarpa were examined. Transmission of the B. macrocarpa alleles into the progeny was strongly dependent on whether F1 hybrids were used as male or female parents in the backcrosses. Distorted segregations occurred in most of the markers when F1 hybrids were used as male parents ; consistant deviations from the expected 1 : 1 ratio resulted from an excess of the B. macrocarpa alleles for a linked pair, R and Got-2, and a deficiency of the alleles for Lap and Gdh-2. Anomalous segregations also occurred for Aph-1 and Px-2, depending on parental strains used in the backcrosses. In contrast to these results, the expected Mendelian ratio was observed in all the markers except for R when F1 hybrids were used as female parents. Because of the lowering of the pollen and seed fertilities in the F1 hybrids and no zygotic lethality after germination in the backcrossed progeny, the aberrant ratios appeared to arise from linkage of the markers with genetic factors affecting gametogenesis, pollen functions and embryo development in the hybrids. Of the six markers, Lap was found to be linked to a gene responsible for an abortion of a part of pollen grains. In addition to the disrupted monogenic ratio, two-locus segregations often deviated from the expected ratios from random association of the alleles. It was thus suggested that the causal factors of distortions might have complex multifactorial and multi-chromosomal genetic origins.
