Some enzyme loci showed more complicated patterns. A large fruition of the progeny showed only the paternal Gpi allele( II of 21 in experiment I, 7 of 30 in experiment II, 5 of I 2 in experiment III ) . Because a different C. gigas female was used for each experiment, the C.rivularis phenotype in progeny cannot be plausibly attributed to a null Gpi allele inherited from the mother. A more likely interpretation is that the maternal allele is expressed irregularly or is less stable in the hybrid F1.