| Type | Location | Cis/Trans | Effect |
|---|---|---|---|
| Structural gene mutations | lacZ, lacY | Only affect lacZ or lacY | Alter amino acid sequence of protein encoded by gene in which mutation occurs |
| Regulator gene mutations | lacI | Trans | Affect transcription of structural genes |
| Operator mutations | lacO | Cis | Affect transcription of structural genes |
| Promoter mutations | lacP | Cis | Affect transcription of structural genes |