Although there is no general theory of gene regulation that allows one to predict the type of mechanism that might be expected to evolve for a given set of genes in a given organism, .some of the elements of such a theory are beginning to emerge as a result of mathematical analysis. Two such elements that help us to understand coupled circuits of gene regulation are treated. First is the "demand theory" of gene regulation.
It provides rules for predicting the modality of gene regulation --that is, whether the molecular mechanism will be positive or negative. Second is the "circuit theory" of gene regulation, which provides rules for predicting patterns of regulatory interactions.
The patterns are enumerated for an inducible system and those that are physically realizable are distinguished from those that are not.