Read the passage carefully and answer the given questions.

Recombinant DNA Technology

Asexual reproduction preserves the genetic information, while sexual reproduction permits variation. Traditional hybridization procedures used in plants and animals breeding very often lead to inclusion and multiplication of undesirable genes along with the desired genes. The techniques of genetic engineering, which include creation of recombinant DNA, use of gene cloning and gene transfer, overcome this limitation and allow us to isolate and introduce only one or a set of desirable genes without introducing genes into the target organism.

Which one of the following is not used as a vector in recombinant DNA technology?

Bacterial chromosomes

The correct answer is Option (3) → Bacterial chromosomes 

In recombinant DNA technology, a vector is a carrier used to transfer foreign genetic material into a host cell. Common vectors include:

• Plasmids – small, circular DNA molecules found in bacteria
• Viruses – like bacteriophages or retroviruses, modified to carry genes
• Cosmids – hybrid plasmid-phage vectors that can carry larger DNA fragments

Bacterial chromosomes are not vectors:

• Bacterial chromosomes are the main genomic DNA of a bacterium, not typically used as a tool for gene transfer.
• They're large, complex, and not easily manipulated like plasmids or cosmids.
• They're the host's own DNA, not an independent, mobile genetic element.

So, while the chromosome receives the inserted gene in some cases, it is not used as a vector.