A cosmid is formed by the combination of the cos sequence of a lambda phage and a plasmid. These cosmids are typically employed in the techniques of genetic engineering as a cloning vector. The sequences of DNA in the cosmids are derived from the lambda phage. They were first described in 1978 and are now used in building genomic libraries. These hybrid plasmids contain 37-52 kilobases of DNA and this capacity is based on the packaging size of the lambda phage.
If these bacteriophages get a suitable origin of replication, they can replicate as plasmids. They can also be packaged into the structures like phage capsids which are then transferred into the cells of the bacteria by the process of transduction and this is performed in the laboratories.
