Plant & Animal Genome IX Conference

Workshop: Brassicas
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INTEGRATING THE GENETIC AND PHYSICAL CHROMOSOME MAPS OF BRASSICA OLERACEA

¹ The University of Birmingham, Birmingham, B15 2TT, United Kingdom

² Horticulture Research International, Wellesbourne, CV35 9EF, United Kingdom

Linking genetic maps constructed with molecular markers to the corresponding physical maps is an important goal in the investigation of crops. Using fluorescence in situ hybridisation (FISH) it is possible to locate single copy genes or longer sequences onto the chromosomes, generating molecular cytogenetic maps. This type of physical map relates molecular markers to the organisation of the chromosomes, and has been shown to correlate well with the molecular physical map (sequence map) for Arabidopsis, but as expected shows differences to the genetic map. For Brassica oleracea, as a first step we have produced a partial karyotype based on the combination of chromosome size, arm ratios and the location of repeated 45S rDNA ,5S rDNA and pericentromeric heterochromatin sequences by FISH. We have mapped one 45S rDNA and the 5S rDNA locus to LGO4 of a B. oleracea map, but were unable to map the remaining two rDNA loci to the genetic map because of the lack of polymorphisms. This cytogenetic map provided us with a framework for further physical mapping. Our next strategy used BACs, cosmids and RFLPs, with known genetic map positions, as probes to identify linkage group associated markers for the remaining chromosomes. The construction of a definitive karyotype, with all linkage groups assigned to our cytogenetic map has been completed. It is clear from the results we have obtained to date, that FISH is an ideal tool with which to integrate the genetical and molecular cytogenetic maps, and will become increasingly important for plant breeding and map based cloning.