Which of the following features are required to facilitate cloning?
(A) Presence of origin of replication (Ori) in the cloning vector
(B) Presence of a selectable marker in the cloning vector
(C) Presence of a single recognition site (preferably) for restriction enzyme in the cloning vector
(D) Presence of more than two promoter regions in the cloning vector
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A), (B) and (C) only
A cloning vector is a DNA molecule, such as a plasmid, that carries a foreign gene into a host cell and multiplies there. The book lists the features a vector needs for cloning.
(A) Presence of origin of replication (Ori) in the cloning vector Correct. Ori is the sequence where replication starts. Any DNA joined to it can multiply inside the host, and it also controls how many copies are made.
(B) Presence of a selectable marker in the cloning vector Correct. A selectable marker, such as a gene for resistance to ampicillin or tetracycline, helps to pick out the host cells that took up the vector and to remove the others.
(C) Presence of a single recognition site (preferably) for restriction enzyme in the cloning vector Correct. The foreign DNA is joined at this site. More than one site would cut the vector into several pieces and make cloning difficult.
(D) Presence of more than two promoter regions in the cloning vector Incorrect. A promoter is where RNA polymerase binds to start transcription. Extra promoters are not among the features needed for cloning, which are the ori, the selectable marker and the cloning sites.
NCERT Extract:
Cloning Vectors – “… The following are the features that are required to facilitate cloning into a vector.
(i) Origin of replication (ori) : This is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA. So, if one wants to recover many copies of the target DNA it should be cloned in a vector whose origin support high copy number.
(ii) Selectable marker : In addition to ‘ori’, the vector requires a selectable marker, which helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants. …
(iii) Cloning sites: In order to link the alien DNA, the vector needs to have very few, preferably single, recognition sites for the commonly used restriction enzymes.”