IDENTIFICATION OF THE A-GENOME AND C-GENOME OF AMPHIDIPLOID BRASSICA-NAPUS (OILSEED RAPE)

A genetic linkage map consisting of 399 RFLP-defined loci was generate d from a cross between resynthesized Brassica napus (an interspecific B. rapa X B. oleracea hybrid) and ''natural'' oilseed rape. The majori ty of loci exhibited disomic inheritance of parental alleles demonstra ting that B. rapa chromosomes were each pairing exclusively with recog nisable A-genome homologues in B. napus and that B. oleracea chromosom es were pairing similarly with C-genome homologues. This behaviour ide ntified the 10 A genome and 9 C genome linkage groups of B. napus and demonstrated that the nuclear genomes of B. napus, B. rapa, and B. ole racea have remained essentially unaltered since the formation of the a mphidiploid species, B. napus. A range of unusual marker patterns, whi ch could be explained by aneuploidy and nonreciprocal translocations, were observed in the mapping population. These chromosome abnormalitie s were probably caused by associations between homoeologous chromosome s at meiosis in the resynthesized parent and the F-1 plant leading to nondisjunction and homoeologous recombination.