Four steps in a newly discovered biochemical pathway in Neurospora are shown below. Capital letters R, T, M and Q are intermediates in the pathway that ends with biosynthesis of the product P. Each arrow represents a step catalyzed by an enzyme composed of a single polypeptide. Six strains (a, b, c, d, e, and f), each carrying a single mutation, were independently isolated.

A. What results do you expect if pairwise complementation tests are done for all combinations of the mutant strains?

B. What results do you expect when each strain is grown in minimal media supplemented with each intermediate in the pathway?

C. Assuming that complementing mutations assort independently in crosses, what percentage of prototrophs are expected among progeny from the following matings? 

(1) a x e (single mutants) 

(2) a f (double mutant) x d (single mutant)

(3) a b (double mutant) x a e (double mutant)

D. Crossing strain b with strain f yields 0.004% prototrophs. What is the distance between mutation sites in these strains?

b,f R T M > d a c,e Q P