iGenetics 3rd Edition by Peter Russell

Exercise 9

Mutants were instrumental in elaborating the model for regulation of the lac operon.
a. Discuss why P lac - and lacO c mutants are cis -dominant but not trans -dominant.
b. Explain why lacI S and lacI -d mutants are trans- dominant to the wild-type lacI + allele but lacI - mutants are recessive.
c. Discuss the consequences of mutations in the repressor gene promoter as compared with mutations in the structural gene promoter.