(a) Differentiate between exons and introns.
(b) What is a plasmid? Why is it selected as vector?

Explanation

Exons : The coding sequences or expressed sequences are defined as exons, Exons are said to be those sequence that appear in mature or processeds RNA.
lntrons : The: exons are interrupted by introns. Introns or intervening sequences and do not appear in mature or processed RNA.
(b) The construction of the first recombinant DNA emerged from the possibility oflinking a gene encoding antibiotic resistance with a native plasmid. The cutting of DNA at specific locations became possible with the discovery of the so-called molecular scissors-restriction enzymes. The cut piece of DNA was then linked with the plasmid DNA. These plasmid DNA act as vectors to transfer the piece of DNA attached to it. Mosquito acts as an insect vector to transfer the malarial parasite into human body. In the same way, a plasmid can be used as a vector to deliver an alien piece of DNA into the host organism.