Question

I^- CAP^- CBS⁺  P⁺ O^C Z⁺ Y⁺    /   
I^S CAP^- CBS⁺  P⁺ O⁺ Z⁺ Y⁺

Describe the genotype and phenotype from the above with respect to the repressor. Some terms you may want to consider (but do not have to include all of) are: homozygous, heterozygous, hemizygous, dominant, recessive, gain-of-function, loss-of-function,

Answer 1

I^S is the dominant mutation. It encodes the super repressor. The super repressor can not bind to the inducer. It will always remain bind to the operator region.

In this genotype, the I gene is in heterozygous conditions. The I^s gene is found to be dominnat in form. It is a kind of loss of function mutant because mutant repressor can not make the wild type repressor protein.

Phenotype is super repressor. The repressor remains bind to the operator region.

Overall there ia found continuous expression of Z and Y genes. Because operator is constitutive in expression. The constitutive operator does not allow repressor to bind to it. Hence RNA polymerase binds to the promoter region. It will proceed further to the structural genes. There is found expression of Z and Y gene. Z gene encodes beta galactosidase. Y gene encodes permease.