A phagemid is a normal plasmid which derived from a coliphage and a plasmid. It carries both a plasmid replication origin allowing isolation of double stranded plasmid from the cytoplasm of cells, and a replication origin usually from a single stranded phage such as f1, fd or M13 which allows the plasmid to enter a single strand replication mode in which only one of the strands is packaged into the virus particle when helper phage is added to the cell.