With the objectives of genetic improvement of the Pacific abalone, Haliotis discus hannai, a series of genetic studies was initiated. Myogen of shell muscle and esterases of digestive diverticula were studied by starch-gel electrophoresis. The results indicated monomorphism in the former and polymorphisms in four loci of the latter. In each of the F and M loci (genetically independent of each other) of the esterases, three codominant alleles that determine six possible phenotypes were postulated.
Phenotypic incidences of samples taken from a wild population from Iwate Prefecture were analyzed on the basis of S. Wright's and Hardy-Weinberg's Laws of Equilibrium. The homozygote excess in esterase F locus suggested an inbreeding structure in the wild population and led to an estimation of the inbreeding coefficient. An overdominance of heterozygotes in esterase M locus and its association with age groups were observed. On the basis of the ratios between the observed incidences of phenotypes and the expected figures, corrected by the inbreeding coefficient, fitness values were calculated for zygotes of M locus.