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Transduction Mechanism in Gene Recombination

	Transduction Mechanism in Gene Recombination A third mechanism by which the genetic material in bacteria can be transferred from one cell to another is through the mediation of bacterial viruses an this process is known as transduction. This process was first discovered by Norman Zinder and J. Lederberg in 1952 during their experiments to see whether the process or conjugation existed in Salmonella. In doing the 'D' tube' experiments, they found that the recombinants appeared only in one arm of the tube without cell contact, Also, cell free filtrates from One culture could yield recombinants when mixed with the other. The active factor in the filtrate was however, resistant to DNase and this ruled out transformation involving DNA.
It was subsequently proved that the active component was a bacteriophage which was carried by one of the strains in the prophage condition. Some bacteria have the ability to carry phage DNA within their own DNA and such bacteria are known as lysogenic bacteria. In such lysogenic bacteria, the prophage under certain conditions becomes active, multiplies and destroys the host cell with the release of a number of phage particles.
The phage particles released from a small number of bacterial cells attack sensitive cells, multiply and release more phage particles. The lysogenic strains are however, resistant to the same phage that they carry. Sometimes when the prophage is released as the vegetative phage, in addition to its own DNA it also carries a small fragment of the host DNA. These phages can infect other bacteria and carry the bacterial DNA to the recipient cells. Such phages are called "transducing phages" and these act as carriers of bacterial DNA from one cell to another.
The size of the DNA transferred by transduction is small as compared to either transformation or conjugation and the amount of DNA is generally less than one per cent of the bacterial genome. This technique is therefore useful only in determining the relative positions of very closely located markers and to map regions within a gene.

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