Linkage arrangement of restriction fragment length polymorphism loci in Brassica oleracea

A detailed genetic linkage map of Brassica oleracea was constructed based on the segregation of 258 restriction fragment length polymorphism loci in a broccoli × cabbage F2 population. The genetic markers defined nine linkage groups, covering 820 recombination units. A majority of the informative genomic DNA probes hybridized to more than two restriction fragments in the F2 population. "Duplicate" sequences having restriction fragment length polymorphism were generally found to be unlinked for any given probe. Many of these duplicated loci were clustered non-randomly on certain pairs of linkage groups, and conservation of the relative linkage arrangement of the loci between linkage groups was observed. While these data support previous cytological evidence for the existence of duplicated regions and the evolution of B. oleracea from a lower chromosome number progenitor, no evidence was provided for the current existence of blocks of homoeology spanning entire pairs of linkage groups. The arrangement of the analyzed duplicated loci suggests that a fairly high degree of genetic rearrangement has occurred in the evolution of B. oleracea. Several probes used in this study were useful in detecting rearrangements between the B. oleracea accessions used as parents, indicating that genetic rearrangements have occurred in the relatively recent evolution of this species.