The inheritance of albinism in a freshwater snail, Physa heterostropha.

Complementation tests revealed that albinism in four laboratory strains of Physa (Physella) heterostropha pomilia resulted from two recessive, nonallelic genes. F2 dihybrid progeny displayed the 9:7 ratio classically associated with reciprocal recessive epistasis between unlinked loci. This offers a contrast to the situation in the better known planorbid snails and provides a valuable tool for the study of reproductive biology in these facultatively self-fertilizing hermaphrodites.