Question

Which of the following features are required to facilitate cloning into a vector?

a. Origin of replication (ori)
b. Selectable marker
c. Cloning site

• A. a, b and c
• B. a and c
• C. b and c
• D. a and b

Answer 1

The correct option is A a, b and c

Vectors are the DNA molecules which can carry the foreign DNA fragment into the host cells for cloning. Examples include plasmids.

Common features of an ideal vector include the following:

• Presence of origin of replication (ori)
• Selectable markers
• Sites for the action of restriction endonucleases (restriction sites or cloning sites)
• Small sizes
• Copy number

The ori site or origin of the replication site is a specific nucleotide sequence on the vector DNA that initiates replication, without being dependent on genomic DNA for replication. Any piece of DNA when linked to this sequence can be made to replicate within the host cells.

Selectable marker is a gene in a vector that helps in the selection of transformants (host cells which have successfully taken up the foreign DNA) and non-transformants (cells which have not taken up the vector DNA).

For example, antibiotic resistance genes in the vector act as selectable markers because they confer antibiotic resistance to the transformants while the non-transformants remain susceptible to antibiotics.

Recognition sites or cloning sites are specific nucleotide sequences, present on the plasmid DNA, that can be recognised and cleaved by restriction endonucleases for incorporation of the gene of interest.

Hence the correct option is
d. a, b and c