The DNA used as a carrier for transferring a fragment of foreign DNA into a suitable host is called vehicle DNA or cloning vector or gene carrier. The 27 plasmid (tumour inducing plasmid) is present in Agrobacterium tumefaciens, a Gram negative soil bacterium that infects a wide range of plants and causes tumorous growth specially at the root /stem junction (crown gall). The 27plasmid comprises the gene responsible for the tumorous growth, gets incorporated into the genome of infected plant cells. This property is of interest foR genetic engineering as Ti plasmid can be use as DNA vector by replacing the tumour inducing genes with the gene of interest and a marker gene to enable selection of transformed cells. The Ti plasmid, is widely used in plant genetic engineering as a vector, novel plant genes being spliced into the plasmid sequence by gene manipulation and thus carried into the host plant cells. This provides the opportunity to develop new and better species.