What is the ultimate objective of $r-DNA$ technology?

Choose the correct statement:
$P -$ Endonucleases cut the $DNA$ at a specific site inside the $DNA$.
$Q -$ $A$ stirred-tank reactor is usually square in shape.
$R -$ In order to force bacteria to take up the plasmid,the bacterial cells must first be made 'competent' to take up $DNA$ by treating them with a divalent cation like $Ca^{2+}$.

Which of the following method$(s)$ is used to introduce foreign $DNA$ into host cells?

When foreign $\text{DNA}$ is inserted into any vector,it results in inactivation of any marker gene. This is used for selection of $......\ :-$

The prerequisites for the biotechnological production of antibiotics are:

Which one of the following statements is not true regarding the gel electrophoresis technique?