Which enzyme is used to synthesize a $cDNA$ probe from a messenger $RNA$ molecule?

Manipulation of $DNA$ in genetic engineering became possible due to the discovery of

The function of a restriction endonuclease enzyme is to:

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 scientist who first discovered the restriction endonuclease is .......

Normal $E.$ coli cells carry resistance against which of the following antibiotics?