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Select the two correct statements out of the four (a-d) given below about lac operon.

(i) Glucose or galactose may bind with the repressor and inactivate it

(ii) In the absence of lactose the repressor binds with the operator region

(iii) The z-gene codes for permease

(iv) This was elucidated by Francois Jacob and Jacque Monod

The correct statements are: 

  • Option 1)

    (ii) and (iii)

  • Option 2)

    (i) and (iii)

  • Option 3)

    (ii) and (iv)

  • Option 4)

    (i) and (ii)


Answers (1)

As learnt in

The lac operon -

In lac operon, a polycistronic structural gene is regulated by a common promoter and regulatory genes. 

- wherein

Such arrangements are very common in bacteria and is referred to as operon. 


  Lac operon was proposed by Jacob and Monod. When glucose is present and lactose is absent, the repressor binds with the operator region and prevents transcription.

Option 1)

(ii) and (iii)

This option is incorrect

Option 2)

(i) and (iii)

This option is incorrect

Option 3)

(ii) and (iv)

This option is correct

Option 4)

(i) and (ii)

This option is incorrect

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