Tumors plaque assay

Many tumor viruses do not destroy cells in which they multiply and hence produce no plaques. They induce morphological changes and faster multiplication rate in the infected cells which are known as transformed cells. Colonies of the transformed cells are developed into large foci which are visible by naked eye. Assay by focus formation depends on counting the number of focus-forming units (FFU), which is analogous to plaque formation assay. 

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