The below diagram shows the map of lac operon:
| Part | β-Galactosidase | Permease | ||
| No Lactose | Lactose | No Lactose | Lactose | |
| a | + | + | - | + |
| b | + | + | - | - |
| c | - | - | - | - |
| d | - | - | - | - |
| e | + | + | + | + |
| f | + | + | - | - |
| g | - | + | - | + |
a. Mutations in Oc synthesis β-galactosidase enzyme. Since, the mutant is located in cis configuration to a lac Z+ gene the permease enzyme is inducible. This is because the lac Y+ gene is cis to operator.
b. A mutation in lac P- inhibits the process of transcription. Thus, the genes cis to lac P+ will be transcribed. These genes are cis towards Oc. Hence, the lac Z+ gene is transcribed.
c. The lac Is is a mutant, which is present in trans and prevents transcription.
d. This process prevents transcription from operon, since the gene lac Is is trans-dominant mutant.
e. There is no functional repressor made and the operator region is mutant as well.
f. The genes cis to lac P+ are transcribed when the lac P- prevents transcription. The lac Z+ gene is transcribed when the genes are cis to Oc.
g. Both operators are wild type and the functional copy of lac I will direct repressor synthesis to control the two operons.