Question

A mutant E. coli strain does not express lacZ, even in the presence of lactose. What is a possible genotype of the cells?

Group of answer choices

a. lacI⁺ lacP⁺ lacO⁺ lacZ⁺ lacY⁺ lacA⁺

b. lacl⁺ lacP⁺ lacO⁺ lacZ⁺ lacY⁺ lacA⁺

c. lacI⁻ lacP⁺ lacO⁻ lacZ⁺ lacY⁺ lacA⁻

d. lacI⁺ lacP⁺ lacO⁺ lacZ⁻ lacY⁻ lacA⁺

e. lacI⁻ lacP⁺ lacOc lacZ⁺ lacY⁺ lacA⁺

Answer 1

The possible genotype of the cells is lacI⁻ lacP⁺ lacO⁻ lacZ⁺ lacY⁺ lacA⁻ . The lacI gene, encoding the repressor protein, is mutated, allowing the expression of the lacZ gene even in the presence of lactose. The answer is option C.

Step-by-step explanation:

The possible genotype of the cells in question is lacI⁻ lacP⁺ lacO⁻ lacZ⁺ lacY⁺ lacA⁻ (option c).

According to the information provided, the lacI gene encodes the repressor protein, which is always made and present in E. coli cells. In the absence of lactose, the repressor protein binds tightly to the operator's DNA, blocking the forward movement of RNA polymerase and preventing transcription of the lac operon. The mutation of the lacI gene in this genotype would result in a non-functional repressor, allowing the expression of the lacZ gene and the production of the ß-galactosidase enzyme even in the presence of lactose.