Which bond is formed by $DNA$ ligase to join a plasmid and a foreign $DNA$ fragment?

The characteristics of a molecular probe are
$I.$ very long molecule
$II.$ double-stranded
$III.$ $DNA$ or $RNA$
$IV.$ complementary to a part of the desired gene
The correct pair is

In the gel electrophoresis method . . . . . . .

Which of the following is not used for isolation of $\text{DNA}$ from cells?

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: When a particular restriction enzyme cuts a strand of $DNA$,overhanging stretches or sticky ends are formed.
Reason $(R)$: Some restriction enzymes cut the strand of $DNA$ a little away from the centre of the palindromic site.
In the light of the above statements,choose the correct answer from the options given below:

The first restriction endonuclease was isolated from which of the following?