In Drosophila melanogaster flies may have red (wild-type) or plum eye color, and normal or stubble bristles (less than half normal length). The progeny of a mating between two plum, stubble flies gave the following results:

Plum, stubble 162
Plum, normal 80
Red stubble 84
Red normal 42

Propose an explanation for these results, and show the genotypes of the P and the F1 generations. Show clearly how the phenotypic ratio in the F1 was obtained.