Origin of replication (Ori)
• This is a specific sequence from where replication starts, when any piece of foreign DNA is linked to this sequence.
• The replication occurs inside the host cells. This sequence is also responsible for controlling the copy number of linked DNA.
• A prokayotic DNA has single origin of replication, while eukaryotic DNA may have more than one origin of replication.
• The vector also requires a selectable marker (antibiotic resistance gene) to identify and eliminate non transformants and selectively permit the growth of the transformants.