If you have a gene pathway with three activities, say A, B and C, and you have a mutant where an area of the pathway is affected, what kind of experiment would allow you to distinguish if A, B or C is affected?
Does it make sense to plate the mutant starting with the C source and work backwards and assume if there is growth, then it must be B or A?
To determine which activity (A, B, or C) in the gene pathway is affected in the mutant, you can design an experiment called complementation analysis or epistasis analysis. This experiment involves crossing the mutant with known mutants that have defects in each of the activities (A mutant, B mutant, and C mutant) and observing the phenotype of the progeny.
If the mutant shows a normal phenotype when crossed with any of the A, B, or C mutants, then it suggests that the affected activity in the mutant is different from A, B, and C. However, if the phenotype remains mutant-like in the progeny of a specific cross, it indicates that the affected activity in the mutant is the same as the one being tested.
Plate experiments, on the other hand, can be used to study the growth patterns of organisms under different conditions. However, in the case of gene pathway analysis, plate experiments alone are not sufficient to determine which activity (A, B, or C) is affected in the mutant.
In conclusion, plate experiments can be used to observe the growth or response of mutants on different media, but for specifically distinguishing the affected activity in a gene pathway, complementation analysis or epistasis analysis are more appropriate experimental approaches.