The season and age-related dependence of the distribution of the frequency of alleles and of five polymorphous loci have been studied for eight cultivated samples of the Japanese scallop M. yessoensis (Jay) from Alexeev Bay (Popov Island, Sea of Japan) using polyacrylamide gel electrophoresis. The consistency of the frequency of alleles and of heterozygotes was revealed for samples with an age greater than one year independently of the season and age. Samples of the younger (11 months) mollusks can have reliable deviations of the frequency of allele and of heterozygotes. However, as the sample reaches a certain age, these genetic parameters correspond to values general to the whole population. The episodic influence of ecological factors on the younger age groups of mollusks is discussed.