CHROMOSOMAL LOCALIZATION AND CHARACTERIZATION OF RDNA LOCI IN THE BRASSICA-A AND BRASSICA-C GENOMES

Using fluorescence in situ hybridization, we located ribosomal DNA loc i on prometaphase chromosomes of the diploid species Brassica rapa and Brassica oleracea and their amphidiploid Brassica napus. Based on com parisons of chromosome morphology and hybridization patterns, we chara cterized the individual B. napus rDNA loci according to their presumed origins in the Brassica A and C genomes. As reported in other studies , the sum of rDNA loci observed on B. rapa (AA genome) and B. oleracea (CC genome) chromosomes was one greater than the total number of loci seen in their amphidiploid B. napus (AACC). Evidence is presented tha t this reduction in B. napus rDNA locus number results from the loss o f the smallest A genome rDNA site in the amphidiploid.