Which of the following is an example of a plasmid vector used in gene…

The correct answer is Option (1) → pBR322

A cloning vector carries a piece of foreign DNA into a host cell and can replicate there. Plasmids (small circular DNA outside the bacterial chromosome) and bacteriophages are both used, because both replicate inside bacterial cells. pBR322 is an E. coli cloning vector made from a plasmid; it has an ori and the antibiotic resistance genes amp^R and tet^R.

Option (1) pBR322 — Correct. pBR322 is a plasmid vector of E. coli. Foreign DNA can be joined at one of its restriction sites, for example the BamH I site in the tetracycline resistance gene.

Option (2) Bacteriophage — Incorrect. A bacteriophage is a virus that infects bacteria. It can be used as a vector, but it is a virus, not a plasmid.

Option (3) Retrovirus — Incorrect. Retroviruses are viruses that have been disarmed and are now used to carry desirable genes into animal cells. They are viral vectors, not plasmids.

Option (4) E. coli — Incorrect. E. coli is the host bacterium into which a vector such as pBR322 is put. It receives the recombinant DNA; it does not carry DNA into another cell.

NCERT Extract:
Cloning Vectors – “You know that plasmids and bacteriophages have the ability to replicate within bacterial cells independent of the control of chromosomal DNA.”
Cloning Vectors – “… Similarly, retroviruses have also been disarmed and are now used to deliver desirable genes into animal cells.”
Cloning Vectors – “… For example, you can ligate a foreign DNA at the BamH I site of tetracycline resistance gene in the vector pBR322.”