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Generalised Transduction / Unrestricted Transduction

	Generalised Transduction / Unrestricted Transduction This type of transduction, generalised transduction is a more common event. It is mediated by the prophages that have remained in the cytoplasm as plasmids that are not attached to the chromosome. This occurs in PI phage and many others. The viral DNA lies in the cytoplasm and produces copies of itself for new phage particles. In doing so it may accidentally incorporate small chromosomal segments of bacterial DNA and incorporates these to its own DNA. Some phages may accidentally package only bacterial DNA. In most cases, normal viruses will be liberated from the cell. Occassionally, a virus contains several bacterial genes acquired in the chromosomal segments.
If such a virus infects a new cell, whereupon they will attach to the chromosome and transduce the cell as lysogeny is established. In generalised transduction, the viral DNA enters the lytic cycle and forms new virus particles However, tiny fragments of bacterial chromosome are sometimes incorporated into the DNA of the new viruses or may occasionally replace the viral DNA. This is a random occurrence that may involve any of the bacterial genes, hence the name generalised transduction. Perhaps one phage in a thousand contains bacterial DNA.All bacterial genes are equally available to be picked up by the phage DNA.
When the viral particles are released during lysis, the genes are carried along and on subsequent infection, the genes enter the cytoplasm of the new host cell where they will now function.The phenomenon of lysogeny is well established in modern microbiology. Diphtheria organisms are known to contain bacteriophages that code for the toxin produced during disease. Herpes simplex viruses remain for many years as prophages in the cytoplasm of the body cells, expressing themselves at, long intervals. Certain viruses are known to attach to human chromosomes, transforming the cells to tumour cells.

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