→ Mostly plasmid and bacteriophage is used as a cloning vector.
→ Plasmid and bacteriophage have the potential to replicate independently in the host cell without having control of chromosomal DNA.
→ In each cell there are plenty of copies of bacteriophage which contains many copies of their genome.
→ In certain bacteria, there are one or two copies of plasmid.
→ Whereas others may have 15-100 copies per cell. Their numbers can go even higher.
→ If we are able to link an alien piece of DNA with bacteriophage or plasmid DNA, we can multiply its numbers equal to the copy number of the plasmid or bacteriophage.
→ Vectors used at present, are engineered in such a way that they help easy linking of foreign DNA and selection of recombinants from non- recombinants.wm