regulation of the lac operon by a repressor is referred to as negative regulation . In this system, the repressor protein is constitutively synthesised and binds to the operator region to prevent transcription . When an inducer (such as lactose or allolactose) is present, it binds with the repressor, inactivating it and allowing RNA polymerase access to the promoter so that transcription can proceed . This interaction is fundamental to the switching mechanism of the operon. Understanding these gene regulation concepts is vital for medical aspirants, as NCERT textbooks serve as the definitive source for approximately 95% of NEET Biology questions .