The lactose present in the growth medium of bacteria is transported to the cell by the action of

$A$ : Single $DNA$ dependent $RNA$ polymerase catalyses transcription of all types of $RNA$ in all except bacteria.
$R$ : Structural genes in bacteria are monocistronic.

Write an explanatory note of gene expression.
 

Select the two correct statements out of the four $(i-iv)$ 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.

How many of the given statements $(i-iv)$ is/are correct?

$i.$ In transcription, adenosine pairs with uracil.

$ii.$ Regulation of lac operon by repressor is referred to as positive regulation.

$iii.$ The human genome has approximately $50,000\; genes.$

$iv. $ Haemophilia is a sex-linked recessive disease.

Select the $correct$ match :