Four mutant strians of bacteria (1-4) all require substance S to grow (each strian is blocked at one step in the S-biosynthesis pathway). Four plates were prepared with mininmal medium and a trace of substance, S to allow a small amount of growth of mutant cells. on plate A, mutant cells of strain 1 were spred over entire surface of tha agar to form a thin law of bacteria. On plate B, the lawn was composed of mutant cells of strain 2, and so on. On each plate, cells of each of the four mutant types were inoculated over the lawn, as indicated in the figure by the circles. dark circles indicae excellent growth. A strain blocked at a later step in the S substance metabolic pathwa accumulates intermediates that can 'feed' a strain blocked at an earlier step.

What is the order of genes (1-4) in the metabolic pathway for synthesis of substance S ?

Options

A. `2 rarr 4 rarr 3 rarr 1`
B. `2 rarr 1 rarr 3 rarr 4`
C. `1 rarr 3 rarr 4 rarr 2`
D. `1 rarr 2 rarr 4 rarr 3`

Answer

C