All of the following are part of an operon except

Write short note on lac operon
 

$A$ : Lac operon exerts negative control only.
$R$ : The operator is occupied by aporepressor during regulation

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

$A$ : 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

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.