A cloning vector is a small piece of DNA, taken from any organism into which a foreign DNA fragment can be inserted for cloning purposes.
Two features that are required to facilitate cloning into a vector –
• 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 host cells.
• Selectable markers – in addition to the ‘ori’, the vector requires a selectable marker, which helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.
The genes encoding resistance to antibiotics such as ampicillin, chloramphenicol, tetracycline or kanamycin, etc are considered some useful selectable markers for E.coli.
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