Chapter 14, Problem 7EQ

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 lacI gene. You then compare the mutant strain and the merozygote with regard to their $\text{β-galactosidase}$ activities in the presence and absence of lactose. You obtain the following results:

	Addition of Lactose	Amount of $\text{β-Galactosidase}$(% of mutant strain in the presence of lactose)
Mutant	No	100
Mutant	Yes	100
Merozygote	No	100
Merozygote	Yes	100

Explain the nature of the defect in the mutant strain.