COMPARATIVE MAPPING OF ARABIDOPSIS-THALIANA AND BRASSICA-OLERACEA CHROMOSOMES REVEALS ISLANDS OF CONSERVED ORGANIZATION

The chromosomes of Arabidopsis thaliana and Brassica oleracea have bee n extensively rearranged since the divergence of these species; howeve r, conserved regions are evident. Eleven regions of conserved organiza tion were detected, ranging from 3.7 to 49.6 cM in A. thaliana, spanni ng 158.2 cM (24.6%) of the A. thaliana genome, and 245 cM (29.9%) of t he B. oleracea genome. At least 17 translocations and 9 inversions dis tinguish the genomes of A. thaliana and B. oleracea. In one case B. ol eracea homoeologs show a common marker order, which is distinguished f rom the A. thaliana order by a rearrangement, indicating that the line ages of A. thaliana and B. oleracea diverged prior to chromosomal dupl ication in the Brassica lineage (for at least this chromosome). Some c hromosomal segments in B. oleracea appear to be triplicated, indicatin g the need for reevaluation of a classical model for Brassica chromoso me evolution by duplication. The distribution of duplicated loci mappe d for about 13% of the DNA probes studied in A. thaliana suggests that ancient duplications may also have occurred in Arabidopsis. The degre e of chromosomal divergence between A. thaliana and B. oleracea appear s greater than that found in other confamilial species for which compa rative maps are available.