Genetics of growth rate in the American oyster: Absence of interactions among enzyme loci

Abstract

Heterozygosity at seven enzyme loci explains about 4% of the variance in body weight (hence, growth rate) of 1-year-old American oysters ( Crassostrea virginica). The various electrophoretically-detected loci affect body weight independently of each other, and there is not much gametic phase disequilibrium among loci in the natural population that was sampled. Thus, there is considerable evidence for overdominance (interaction of alleles at the same locus) but little evidence for epistasis (interaction of alleles at different loci). As a result, we predict a large dominance component in the variance of growth rates in natural populations, and expect that most of this component will be explainable by the one-locus effects. The independence of enzyme loci increases their value as markers in a selection programme. As more loci are examined, additional information is obtained about possible genome components affecting growth rate, which would not have been true if there had been strong epistatic interactions. This result is valid regardless of whether there is a cause-effect linkage or an associative linkage between the electrophoretic markers and the genes affecting growth rate. In principle, this search is limited only by the number of loci whose products can be detected by electrophoresis or other biochemical techniques, and by the number of loci which are polymorphic in the base population.