One can isolate rare mutations in the lac operator (lacO) gene that produce a non-inducible (super-repressed) phenotype. Like other lacO mutations,...

One can isolate rare mutations in the lac operator (lacO) gene that produce a non-inducible (super-repressed) phenotype. Like other lacO mutations, these mutations (called O^0 ) are cisdominant.

a) Propose a model for the molecular basis of O^0 mutations.

b) Based upon your model, explain why O^0 mutants are cis-dominant. (Consider the situation in O+ /O^0 and in O^c /O^0 .)

c) Based upon your model, make predictions about whether or not O^0 mutations are epistatic to lacI– (constitutive) mutations or to lacI+ (inducible).