Plant & Animal Genomes XI Conference

January 11-15, 2003
Town & Country Convention Center
San Diego, CA

Workshop: Aquaculture
            

LINKAGE AND GENE-CENTROMERE MAPS OF THE PACIFIC OYSTER Crassostrea gigas

Bodega Marine Laboratory, University of California, Davis, Bodega Bay, CA 94923

The Pacific oyster Crassostrea gigas has the highest production and the second highest value of farmed aquatic species, fresh or marine, worldwide. A linkage map, which is a valuable tool for improving commercial stocks, has thus been developed using 100 microsatellite markers. So far, 10 linkage groups have been found, a number that corresponds to the haploid number of chromosomes. The male consensus map has 89 loci and covers 691cM; the female map has 86 loci and covers 752 cM. There are 100 loci in total between both male and female map. We investigate differences in recombination rates among families and map the location of lethal genes segregating in F₃ and F₄ populations. A gene-centromere map of 56 loci was made using six, unrelated, triploid families. Triploidy was induced by chemically inhibiting extrusion of the second polar, which retains maternal sister chromosomes in triploid progeny. If the female is heterozygous for a locus, her progeny will bear two copies of only one maternal allele unless there has been a crossover between the marker and the centromere. Young larvae (6 and 11 days) were examined for 56 loci, of which 52 were previously mapped, two were not linked, and two were not tested before. Proportions of heterozygous progeny (y) greater than 0.67 occurred for 19% of loci, which indicates positive interference occurring after the formation of a single chiasma. Sixty-four percent of loci have a y-value between 0.1 and 0.66, while 16% of loci have y-values less than 0.1. Comparison of gene-centromere and linkage maps reveals some discrepancies between the two.