Viruses replicating themselves in the bacterial cells are known as phages. They are capable of surviving through a different mechanism. Their genes are easy to study since these entities are totally dependent on the bacteria. Plus they naturally exhibit the property of recombination of genetic material. Thus bacteriophage gene mapping is an interesting topic for geneticists. These phages are vectors since they are capable of transferring the genetic material from one bacterial cell to another bacterial cell. They are model organisms used in biological research. A gene map is a linear designation of mutant sites within a gene based on intragenic recombination. It could exhibit a sequence with regulatory sites, introns, exons and other elements. The principles used in eukaryotic gene mapping are applicable for mapping phage genes. Two main principles follow this. The genetic material gets exchanged between strains differing in the genetic markers. The second principle involves the detection of recombinants and counting them.