Biology · Biotechnology: Principles and Processes · NEET
No. A plasmid is a natural, small, circular, double-stranded, extra-chromosomal DNA found in bacteria. It becomes a cloning vector only after scientists modify it to carry useful features like an origin of replication, selectable markers and a cloning site. So all cloning vectors used in labs like pBR322 are plasmids, but a wild plasmid is not automatically a ready-to-use cloning vector.
A naked piece of foreign DNA cannot copy itself inside a host cell because it has no origin of replication and the cell may destroy it. The vector supplies the origin of replication (ori), so once the gene is joined to the vector, the host copies both together. This is why NCERT says the vector is what makes multiplication of the gene of interest possible.
The gene of interest (foreign or alien DNA) is the piece you actually want to copy or express. The cloning vector is the carrier DNA that transports it and gets it replicated inside the host. Enzymes like DNA ligase join the two to make recombinant DNA. In an exam, remember: vector = carrier, insert = passenger.
Yes. Bacteriophages (like lambda phage) are used as cloning vectors because they infect bacteria and multiply very fast, giving high copy numbers. Plasmids and bacteriophages are the two classic bacterial cloning vectors in NCERT. For animal cells retroviruses are used, and for plants the Ti plasmid of Agrobacterium.
No. A probe is a labelled single-stranded DNA/RNA used to detect a complementary sequence by hybridisation, and a restriction enzyme is molecular scissors that cut DNA. Neither carries or replicates a gene, so neither is a cloning vector. NEET 2023 directly tested this by asking which option is NOT a cloning vector.
Which of the following is not a cloning vector?
Which of the following is not a feature of the plasmids?
Which of the following is commonly used as a vector for introducing a DNA fragment in human lymphocytes?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A cloning vector is a DNA molecule that carries a foreign DNA fragment into a host cell and enables its replication (copying) there.
Plasmids (for example pBR322) and bacteriophages such as lambda phage. For plants the Ti plasmid of Agrobacterium and for animal cells disarmed retroviruses are used.
A plasmid is a natural circular extra-chromosomal DNA in bacteria. A cloning vector is any DNA (often a modified plasmid) engineered with ori, markers and a cloning site to carry and copy a foreign gene.
DNA ligase joins the foreign DNA and the cut vector, after both are cut by the same restriction enzyme to give matching sticky ends, forming recombinant DNA.
Because it is small, replicates independently of the bacterial chromosome, is easy to isolate, and can be transferred into host cells, allowing the linked gene to be copied many times.
