Identify the correct statements regarding features of a vector.
A. They should have ability to replicate within the host
B. They should have 'ori' sites that start replication
C. Its origin should not support high copy number
D. They should have more than one recognition sites for restriction enzymes
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A and B only
A. They should have ability to replicate within the host — Correct. A vector must multiply inside the host cell, so that the linked DNA is multiplied with it.
B. They should have 'ori' sites that start replication — Correct. Ori is the sequence where replication starts; any DNA linked to it can be replicated.
C. Its origin should not support high copy number — Incorrect. The ori also controls the copy number; to get many copies of the target DNA, a vector with an ori that supports a high copy number is chosen.
D. They should have more than one recognition sites for restriction enzymes — Incorrect. A vector needs very few, preferably single, recognition sites for the enzymes used. More sites would cut the vector into several pieces.
NCERT Extract:
Cloning Vectors – “… (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.”
Cloning Vectors – “… (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.”