Human beings suffer from more than 5000 different diseases caused by single gene mutations, e.g., Cystic fibrosis, Acatalasia, Huntington,s chorea, Tay sach,s disease etc. Gene therapy may be defined in broad general terms as follows: introduction of a normal functional gene into cells, which contain the defective allele of the concerned gene with the objective of correcting a genetic disorder.
Bacteriophages are viruses that attack bacteria. Several bacteriophages are used as cloning vectors, the most commonly used E.Coli phages being lambda and M13 phages. Phage vectors present two advantages over plasmid vectors, (1) they are more efficient than plasmids for cloning of large DNA fragments (2) it is easier to screen a large number of phage plaques than bacterial colonies for the identification of recombinant clones.