Suppose that you have isolated a mutant strain of E. coli in which the lac operon is constitutively expressed. To understand the nature of this defect, you create a merozygote in which the mutant strain contains an F′ factor with a normal lac operon and a normal lacI gene. You then compare the mutant strain and the merozygote with regard to the amount of β-galactosidase produced in the presence and absence of lactose. You obtain the following results:

Explain the nature of the defect in the mutant strain.

Addition of Lactose Amount of -Galactosidase (% of mutant strain in the presence of lactose) Mutant No Mutant Yes 100 100 Merozygote No 100 Merozygote Yes 200