A cloning vector is a small piece of DNA that can be used to carry a foreign DNA into another cell for cloning purposes. The foreign DNA is inserted into the cloning vector, which can then be replicated and expressed inside the host cell. Cloning vectors possess several features that make them useful for this purpose, including:

• Origin of replication: A cloning vector should possess an origin of replication so that it can self-replicate inside the host cell.

• Restriction site: It should have a restriction site for the insertion of the target DNA.

• Selectable marker: It should have a selectable marker with an antibiotic resistance gene that facilitates screening of the recombinant organism.

• Small size: It should be small in size so that it can easily integrate into the host cell.

• Large DNA insertion: It should be capable of inserting a large segment of DNA.

• Multiple cloning sites: It should possess multiple cloning sites.

• Compatibility: It should be capable of working under the prokaryotic and eukaryotic systems.

There are different types of cloning vectors, including plasmids, bacteriophages, cosmids, and bacterial artificial chromosomes (BACs) . Plasmids were the first vectors used in gene cloning and are found in bacteria, eukaryotes, and archaea. Cloning vectors can be modified to include genes that are useful for cloning and manipulating other genes. All commonly used cloning vectors in molecular biology have key features necessary for their function, such as a suitable cloning site and selectable marker.