In figure 6-15,
a) Double mutant is present in the panel (d) that is mutated both in the regulatory protein and the structural protein. The double mutant obtains when intercrossing occurs.
b) The regulatory gene produces protein that binds to the regulatory region present upstream in a specific gene and enabling it to be transcribed. In the absence of the regulatory gene, the target gene would be transcribed at very low levels.
c) No. Since the regulatory protein is highly necessary to initiate the transcription of the specific protein, the protein product from the active gene will not be produced.