Final answer:
The lacI gene is not controlled from the same promoter as the lacZ gene, as they have distinct functions; lacI is a regulatory gene with its own promoter. A mutation in a structural gene like lacZ would impair lactose metabolism due to reduced production of a critical enzyme.
Step-by-step explanation:
The statement that the lacI gene is controlled from the same promoter as the lacZ gene is false. The lac operon consists of the structural genes lacZ, lacY, and lacA, which code for proteins involved in lactose metabolism, and these are different from the regulatory gene lacI. The lacI gene has its own promoter and produces a repressor that can bind to the operator site to regulate the expression of the lac operon. A mutation in one of the structural genes, like lacZ, would disrupt the production of the corresponding enzyme, such as ß-galactosidase, which is crucial for the metabolism of lactose into glucose and galactose. As a result, E. coli would have trouble utilizing lactose as an energy source.