Plant & Animal Genome IX Conference

Workshop: Aquaculture
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TRANSMISSION OF RECESSIVE DELETERIOUS MUTATIONS IN HYBRID F3 AND F4 FAMILIES OF THE PACIFIC OYSTER Crassostrea gigas.

¹ Bodega Marine Laboratory, University of California, Davis, Bodega Bay CA 94923 USA

² Laboratoire de Genetique des Poissons, INRA 78352 Jouy en Josas, France

The genetic basis of heterosis and genetic load is investigated in the Pacific oyster. Previous work on seven experimental hybrid F2 and F3 families showed that there are at least 12-14 lethal genes per individual. This number was determined using segregation distortion at linked microsatellite markers and is consistent with the number of lethal genes estimated for pine trees. There are two hypotheses to account for the presence of this high genetic load: a high background rate of recessive deleterious mutation, or epistatic interactions creating synthetic lethals. This study examines whether the load is mutational or segregational. If mutational, then the lethal alleles should be predictably transmitted to the next generation. Specifically, a mating between two lethal-allele carriers, should result in a deficiency of homozygote genotypes in the progeny. If the load is segregational, then the same mating might not yield a distortion of segregation because of recombination. We tested these hypotheses by following segregation patterns in the offspring of lethal-allele carriers in F3 and F4 families. We looked for Mendelian segregation in larval, juvenile, and adult stages. In one case, the cross AA x AB (where A is hypothetically linked to the recessive allele) showed Mendelian segregation ratios at day 11, and at day 25, the ratio was 0.36:1. These results are consistent with the previous generation at the same locus for two-month old juveniles. Additionally, it appears that distortion is coincident with metamorphosis, suggesting that this linked lethal gene is expressed at metamorphosis.