Integration of the cytogenetic and genetic linkage maps of Brassica oleracea.

We have assigned all nine linkage groups of a Brassica oleracea genetic map to each of the nine chromosomes of the karyotype derived from mitotic metaphase spreads of the B. oleracea var. alboglabra line A12DHd using FISH. The majority of probes were BACs, with A12DHd DNA inserts, which give clear, reliable FISH signals. We have added nine markers to the existing integrated linkage map, distributed over six linkage groups. BACs were definitively assigned to linkage map positions through development of locus-specific PCR assays. Integration of the cytogenetic and genetic linkage maps was achieved with 22 probes representing 19 loci. Four chromosomes (2, 4, 7, and 9) are in the same orientation as their respective linkage groups (O4, O7, O8, and O6) whereas four chromosomes (1, 3, 5, and 8) and linkage groups (O3, O9, O2, and O1) are in the opposite orientation. The remaining chromosome (6) is probably in the opposite orientation. The cytogenetic map is an important resource for locating probes with unknown genetic map positions and is also being used to analyze the relationships between genetic and cytogenetic maps.