Define transformation in Griffith's experiment. Discuss how it helps in the identification of DNA as the genetic material.

1.The experiment was performed in the year 1928 by Frederick Griffith.

2. Griffith used two strains of bacteria Streptococcus Pneumoniae.

3. These were the S-strain (smooth strain) and the R-strain (rough strain) .

4. These strains were then injected into two different mice.

5. He found that only mice injected with S-strain had the disease and was virulent. This was because the S-strain has a polysaccharide covering which protected the strain from mice’s immune system.

6. The R--strain mice did not have the disease and was non-virulent. This was because the R-strain did not have the covering which protected the strain from mice’s immune system.

7. After this, a combination of heat killed S-strain and live R-strain were injected into two different mice.

8. The disease was seen in the mice.

9. Through this Griffith showed that the transformation took place.

10. Some ‘transforming principle’ of the S-strain was picked up by the R-strain which transformed the R-strain to the S-strain and made it virulent. This change in R-strain showed that it was the inherited genetic material.

11. This genetic change was permanent which further showed that DNA was the genetic material.