OVERVIEW OF PROGRESS IN GENOME MAPPING IN OYSTERS

College of Marine Studies, University of Delaware, Lewes, DE 19958 USA

Selective breeding programs are underway in several countries to develop improved strains of two economically important species of cupped oyster, the Pacific oyster Crassostrea gigas and the eastern oyster Crassostrea virginica. For both species, a number of reference families have been established to facilitate coordinated efforts to develop linkage maps. For C. gigas, a number of allozyme and microsatellite loci have been developed; for C. virginica, allozyme and anonymous nuclear DNA loci are presently available, with efforts to develop microsatellite markers in progress. Some loci display aberrant segregation ratios, arising apparently from nonrandom mortality occurring during early developmental stages. Future efforts will focus on collection of multilocus genotypic data from early zygotic stages in order to obtain less biased data for mapping studies. The current status of marker development and linkage maps for both Crassostrea species will be discussed.