In a cross of limnaea, the snail contributing the eggs was dextral but of unknown genotype. both the genotype and the phenotype of the other snail are unknown. all f1 offspring exhibited dextral coiling. ten of the f1 snails were allowed to undergo self-fertilization. one-half produced only dextrally coiled offspring, whereas the other half produced only sinistrally coiled offspring. what were the genotypes of the original parents?