Structural gene is monocistronic $- P$
Structural gene is polycistronic $- Q$
Select the correct option for $P$ and $Q$.
$\quad\quad\quad P \quad\quad Q$

Which of the following statements concerning the regulatory gene $(i)$,associated with the $lac$ operon are incorrect?
$(I.)$ $\text{mRNA}$ is transcribed from the $i$ gene whether lactose is present or not.
$(II.)$ $\text{mRNA}$ is transcribed from the $i$ gene only when the lactose is present.
$(III.)$ $\text{mRNA}$ is transcribed from the $i$ gene only when the lactose is not present.
$(IV.)$ Lactose inhibits the translation of $i$ gene $\text{mRNA}$.

$Y$ gene in $lac$ operon is responsible for .....

$A$: Operator gene is functional when it is not blocked by repressor.
$R$: Regulator gene produces active protein only which acts on operon system in $E. coli$.

The 'Operon model' for gene regulation in bacteria was proposed by:

In the tryptophan operon,which of the following statements is correct?