Question

Which among the following are features required in a vector to facilitate cloning?
I. It should have ori - a sequence from where replication starts.
II. It should have a selectable marker.
III. It should have several recognition sites for a particular restriction enzyme.
IV. It should have a single recognition site for commonly used restriction enzymes.

• A. I, II
• B. I, II, III
• C. I, III, IV
• D. I, II, IV

Answer 1

The correct option is D I, II, IV

A cloning vector is a DNA molecule which can replicate autonomously. In biotechnology, vectors serve as vehicles to carry the gene of interest.

Every cloning vector should ideally have

1. ori - origin of replication: It is a sequence of DNA from where replication starts. It helps in replication of vectors independently when inserted into host cells.

2. Presence of a selectable marker is important in a vector. The genes encoding resistance to antibiotics are usually considered as selectable markers.

They help in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.

Organisms that have taken up the exogenous DNA from the surrounding environment are called transformants.

Organisms that have not taken up the exogenous DNA from the surrounding environment are called non-transformants.

3. Cloning sites: Cloning site is the recognition site in DNA at which the restriction enzyme binds and makes a cut. Foreign DNA can be inserted within the restriction sites. It is better to have a single recognition site for commonly used restriction enzymes. Presence of more than one copy of the same recognition site within the vector will generate several fragments, which will make gene cloning complicated.