Genetics: Analysis and Principles 4th Edition by Robert Brooker

Exercise 7

Let's suppose 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 lacl gene. You then compare the mutant strain and the merozygote with regard to their -galactosidase activities in the presence and absence of lactose. You obtain the following results:
Explain the nature of the defect in the mutant strain.