Pick the statement that is true. a. cAMP is the inducer for the lac operon. b. In a positive inducible system the activator is transcribe in an active form. c. In the lac operon transcription is initiated by binding the inducer to the promoter. d. A promoter mutation will change the frequency of initiation of operon transcription. e. Tryptophan is an inducer of the trp operon.

Option D

Explanation:

Tryptophan which is an amino acid is an inducer that stimulates the activation of the trp operon. The trp operon describes sequence of genesis that codes for biosynthetic enzymes for the amino acid tryptophan. The trp operon is regulated in such a way that when tryptophan levels are low or when they are high, the operon is expressed (turned "on") or repressed (turned "off") respectively. The trp operon is regulated by the trp repressor (binding of two molecules of tryptophan). Then this complex binds to the operator when tryptophan level is high.

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.