Based upon these crossfeeding results, indicate the order of the G, E, and F genes in the arginine biosynthesis pathway shown below. Briefly explain your rationale for the proposed order. The F mutant accumulates the diffusible intermediate ornithine which is excreted and can be used by the E mutant. The G mutant accumulates the diffusible intermediate citrulline which excreted and can be used by the F and E mutants. Under permissive conditions one mutant only makes heads and the other mutant only makes tails, but you don't know which mutant has each phenotype.
Tails alone can bind to the surface of the bacteria.
However, this scheme will only work if tails are added first, and then heads are added. If heads are added first, they will not bind to the cells and so removed during centrifugation. Thus if a portion of each defective phage is mixed together, a tailed head is produced which contains DNA which is genetically still tail minus. These reconstituted phages are plated out on a lawn of permissive host cells so that plaques form. The phages in these plaques are exclusively tail minus genetically but phenotypically are tailed because of growth in a permissive strain.