While working with a purple flower, you identify a set of mutant flowers that are blue and another set of mutants that are red. You hypothesize that the genes that regulate flower color act together in the biosynthetic pathway displayed below:

Blue pigment --> red pigment --> purple pigment

To test your hypothesis, you cross two heterozygous purple flowers together and observe the offspring. If your hypothesis is correct, which of the following phenotypic ratios do you expect to observe?

a. 9 purple: 3 blue: 3: red: 1 white
b. 9 purple: 3 blue: 4 red
c. 9 purple: 4 blue: 3 red
d. 12 purple: 3 blue: 1 red
e. 12 purple: 1 blue: 3 red
f. 9 purple: 7 white