During the process of isolation of $DNA$,chilled ethanol is added to

When a foreign $DNA$ is introduced into an organism,how is it maintained in the host and how is it transferred to the progeny of the organism?

$A$ probe is used in which stage of genetic engineering?

r-$DNA$ is inserted within the coding sequence of an enzyme,$\beta$-galactosidase. This results in the inactivation of the gene for the synthesis of this enzyme,which is referred to as . . . . . . .

In gel electrophoresis,the $DNA$ fragments separate according to ........

What is the charge on $DNA$ and towards which electrode does it migrate during gel electrophoresis?