AN UPDATE ON PHYSICAL AND LINKAGE MAPPING IN THE EASTERN OYSTER Crassostrea virginica GMELIN

¹ Haskin Shellfish Research Laboratory, Institute of Marine and Coastal Sciences, Rutgers University, 6959 Miller Avenue, Port Norris, NJ 08349, USA

The eastern oyster, Crassostrea virginica Gmelin, supports major fishery and aquaculture industries in the US. In an attempt to develop a basic genomic map for the eastern oyster, work has been conducted to develop tools for physical and linkage mapping. For physical mapping, we used fluorescence in situ hybridization (FISH) for the cytogenetic characterization and mapping of oyster chromosomes. Several repetitive DNA sequences and genes were assigned to oyster chromosomes by FISH, and some revealed interesting features of the oyster genome. The chromosomal location of rRNA genes, on the long arms of Chromosome 10 (10q) in all Pacific species and on the short arms of Chromosome 2 (2p) in all Atlantic species studied so far, provides a divide between the Pacific and Atlantic species. Nine unique sequence probes (P1 clones) were mapped to eight of the ten oyster chromosomes, and more are being mapped. For linkage mapping, we focused on the development and use of amplified fragment length polymorphism (AFLP) markers. Over 500 polymorphic AFLP markers were developed, and a moderately dense linkage map was built. This preliminary map is being used for the mapping of disease-resistance genes in the eastern oyster. Microsatellite and Type I markers are being added to the linkage map. Segregation markers are being developed for the cytogenetically mapped P1 clones. The goal is to integrate the cytogenetic and linkage maps by assigning the same DNA sequences to specific chromosomes and linkage groups.