Plasmid vector in DNA recombinant technology means
(a) a virus that transfers gene to bacteria
(b) extra-chromosomal autonomously replicating circular DNA
(c) sticky end of DNA
(d) any fragment of DNA carrying desirable gene
(b) The vectors are DNA molecules that can carry a foreign DNA segment and replicate inside the host cell. Plasmid vectors are extra-chromosomal, self-replicating, usually circular, double-stranded DNA molecules, found naturally in many bacteria and also in some yeast. Although plasmids are usually not essential for normal cell growth and division, they often confer some traits to the host organisms, for example, resistance to certain antibiotics or toxins that can be a selective advantage under certain conditions. These naturally occurring plasmids have been modified to serve as vectors in the laboratory.