Q.What are the features which requires to facilitate cloning in a vector ?

A cloning vector must have an origin of replication, a selectable marker, unique restriction sites for inserting DNA, and be small and easy to manipulate.

For a vector (such as a plasmid) to efficiently carry and clone a foreign gene inside a host cell, it must possess the following features:

1. Origin of replication (ori): a specific DNA sequence from which replication begins; this allows the vector (and any foreign DNA inserted into it) to replicate autonomously inside the host cell, and also controls the copy number -- the number of vector copies produced per host cell.

2. Selectable marker: a gene (commonly an antibiotic-resistance gene, e.g. for ampicillin or tetracycline) that allows identification and selection of host cells that have successfully taken up (been transformed by) the vector, distinguishing them from untransformed cells, which fail to grow under selective conditions.

3. Cloning sites (unique restriction sites): the vector must have a small number of unique recognition sites for common restriction enzymes, ideally clustered into a multiple cloning site (MCS), where foreign DNA can be inserted using the same restriction enzyme(s) used to cut the DNA of interest -- without disrupting the vector's origin of replication or selectable marker.

4. Small and easily manipulable size: a small vector is easier to isolate from the host, to cut with restriction enzymes, to ligate with foreign DNA, and to reintroduce into a host cell, than a very large DNA molecule would be.

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