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 undesirable genes into the target organism.
Which one of the following is not used as a vector in recombinant DNA technology?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Bacterial chromosomes
A vector is a DNA molecule that carries a foreign gene into a host cell. It must be able to replicate on its own inside the host, so that the gene linked to it is copied too.
Option (1) Plasmid — Used as a vector. A plasmid is a small, circular piece of DNA in a bacterium, outside its main chromosome. It replicates by itself, and pBR322 is a common plasmid vector.
Option (2) Viruses — Used as a vector. Bacteriophages (viruses of bacteria) are used as vectors because they make many copies of their genome inside a bacterium. Disarmed retroviruses are used to carry genes into animal cells.
Option (3) Bacterial chromosomes — Not used as a vector. The main chromosome of a bacterium is its own genome. It is large and cannot be taken out and moved into a host like a vector. The BACs used in the Human Genome Project are bacterial artificial chromosomes, made in the laboratory, not the natural chromosome.
Option (4) Cosmids — Used as a vector. A cosmid is a plasmid that carries the ‘cos’ sites of a bacteriophage. It can be packed into a phage coat and can carry a larger piece of foreign DNA than an ordinary plasmid.
Note: This passage is taken from NCERT as it is. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Cloning Vectors – …
