15. Transcriptional control in which a repressor protein prevents a gene from being expressed is ___________ control. Ans: negative 16. Mutations in the lac operator generally result in _____________ expression of the lac structural genes. Ans: constitutive 17. Binding of the inducer to the lac repressor protein changes its structure so that it has lower affinity for the operator. This is an example of ____________ control. Ans: allosteric 18. A ____________________ regulatory circuit involves an inactive activator that is activated by an inducer.