Consider a biochemical pathway in petal cells of a plant, in which a white precursor is turned into a final red pigment through a yellow and an orange intermediate by the activity of three enzymes encoded by genes A, B, and C. The petal color in plants harboring functional (capital letter) or nonfunctional (lowercase letter) alleles of these genes is presented in the following table. What do you think is the order in which the enzymes act in the pathway? Your answer would be a three-letter string composed of letters A to C, e.g. BCA.

Question

Quizplus · Accepted Answer

With the b allele, the petals are white regardless of whether the other gene products are functional. Hence, B should be acting first. The genotype at the C locus makes a difference only when the active A allele is present, placing C at the last step.

Consider a Biochemical Pathway in Petal Cells of a Plant