Correct option (b) extra-chromosomal autonomously replicating circular DNA
Explanation :
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 the a selective advantage under certain conditions. These naturally occurring plasmids have been modified to sen,e as vectors in the laboratory.
