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?

The repressor region D generates a repressor protein, which combines with the operator region B, thus inhibiting the process of transcription. Hence, a mutated operator region will not be repressed by the repressor protein and the lac gene is articulated constitutively.  

A mutated repressor protein will not be able to combine with the operator region. Therefore, mutation of repressor and operator will result in the expression of the lac gene constitutively.  

In strain 1, a mutated operator region is present. Thus, repressor from F' will not possess the tendency to combine with the operator. Thus, the expression of the lac gene takes place constitutively. There is a sign for repressor, however, the enzyme is expressed.  

In strain 2, a mutated repressor protein is present, and a non-mutated repressor is generated by the F' plasmid. The mutated repressor will not combine with the operator and the articulation of the enzyme takes place, however, the non-mutated repressor protein from F' will combine with the operator and hence, will repress the expression of the gene. There is a sign for repression and the enzyme is repressed.  

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