Two genes interact to produce various phenotypic ratios among F2 progeny of a dihybrid cross. Design a different pathway explaining each of the F2 ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F2 progeny produced by crossing wild-type F1 organisms with the genotype RrTt. 9/16 Dark Blue 6/16 light blue 1/16 white
A) At least one copy of each dominant allele results in dark blue, at least one copy of either dominant allele produces light blue, and the absence of both dominant allele produces white.
B) If both dominant alleles are present, the result is dark blue. At least one copy of one specific dominant allele is required for light blue. If that dominant allele is not present, the result is white, regardless of whether the other dominant allele is present.
C) At least one copy of both dominant alleles results in dark blue; at least one copy of one of the dominant alleles also results in dark blue, but at least one copy of the other dominant allele produces light blue; and the absence of either dominant allele produces white.