Which of the following techniques is most commonly used to separate $DNA$ molecules by size?

The preparatory phase before fermentation is known as:

Assertion : Insertion of recombinant $DNA$ within the coding sequence of $\beta -$ galactosidase results in colourless colonies.
Reason : Presence of insert results in inactivation of enzyme $\beta -$ galactosidase known as insertional inactivation.

Gel electrophoresis is used for:

Recombinant $\text{DNA}$ is directly injected into the nucleus of an animal cell by $-$

Give information about bioreactors.