Mutations in region B and region D give the same results - when either of these regions is mutated, the operon is expressed under all conditions (called constitutive expression). You hypothesize that region B is the operator region and that Region D is the repressor protein. To test your hypothesis, you create two partial diploid lines by introducing a F' plasmid with a wild-type lac operon: Strain 1: F' A B C D E / A B- C D E Strain 2: F' A B C D E / A B C D- E What experimental results would be predicted by your hypothesis

As it is given in the question that region D is the repressor protein and operator region is region B  then the The repressor region D form a protein that will bind to the operator region B and leads to inhibition of the transcription. So, the repressor protein will not repressed a mutant operator and the lac gene will express itself constitutively.

Strain 1:  F' A B C D E / A B- C D E

In this strain the mutant opertor gene is present so, it will not repressed by F' as it will not be able to bind. Hence, the lac gene expression is constitutive.

Strain 2:  F' A B C D E / A B C D- E

In this strain there is two protein produced by the F' plasmid mutated repressor protein, and a non-mutated repressor protein. As we know mutated repressor will not bind to operator gene and still expression will take place but here  a extra not mutated non-mutated protein is present and the repressor protein from F' will bind to the operator region B and thus repress the expression of gene in it.

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