in Molecular Basis of Inheritance by

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  1. Frederick Griffith explained the process of “Transformation” using two bacterial strains (Streptococcus pneumoniae) which had been infected to mice.
  2. One was strain-III S (smooth) and second was Strain-II R (rough). When these strains were infected to mice, III-S strain containing mice died where as II-R strain containing mice lived because III-S strain was virulent and II-R strain was non-virulent.
  3. In the third experiment Griffith applied heat killed smooth strain (III S) into mice, which was non-virulent and mice lived.
  4. In the fourth experiment he applied the mixture of rough strain (II R) and heat killed smooth strain, which was virulent to mice and mice died.
  5. This showed that the type II-R strain had been "transformed" into the virulent type III-S strain by a "transforming principle" that was the part of the dead III-S strain bacteria.
  6. After Griffith’s experiment, Avery-MacLeod-McCarty experiment concluded that DNA extract from a virulent strain of pneumococcus, genetically transformed a non-virulent strain of this organism into a virulent form.
  7. This showed that the transforming genetic element was DNA.
  8. In this way the initiation for identification of DNA was done by Griffith’s experiment.