Question
Describe Griffith’s transformation experiment.
OR
In the light of Griffith’s experiment, explain the action of two strains of streptococcus pneumoniae and give his conclusion.
✓
Answer
(1) In 1928, Frederick Griffith, carried out experiments with bacterium Streptococcus pneumoniae (which causes pneumonia in humans and other mammals).
(2) Griffith used two strains of Streptococcus pneumonia:
- S-type (Virulent, smooth, pathogenic and encapsulated).
- R-type (Non-virulent, rough, non- pathogenic and non-capsulated).
(3) Experiments carried out by E Griffith:
- Mice were injected with R-strain bacteria and they survived (no pneumonia).
- Mice injected with S-strain bacteria developed pneumonia and died.
- When heat-killed S-strain bacteria were injected in mice, the mice survived.
- On injecting a mixture of heat-killed S-bacteria and live R bacteria, the mice died.
(4) Griffith obtained live S-strain bacteria from the blood of the dead mice.
(5) He concluded that the live R-strain bacteria must have picked up something (which he called transforming principle) from the heat killed S bacterium, and got changed into S-type. Transforming principle allowed R-type to synthesize capsule and it became virulent.
(6) Thus, F. Griffith first demonstrated genetic transformations.
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