Question

Describe Griffith's transformation experiment.

Answer 1

1. Frederick Griffith conducted studies with the bacterium Streptococcus pneumoniae (which causes pneumonia in humans and other species) in 1928.
2. Griffith employed two Streptococcus pneumoniae strains.
   
   1. S-type (Virulent, smooth, pathogenic and capsulated).
   2. R-type (Non-virulent, rough non-pathogenic and non-capsulated).
3. Experiments carried out by F. Griffith:
   1. Mice were injected with R-strain bacteria they survived (no pneumonia).
   2. Mice injected with S-strain bacteria developed pneumonia and died.
   3. Mice survived after being injected with heat-killed S-strain bacteria.
   4. The mice died after being injected with a mixture of heat-killed S-bacteria and live R-bacteria. Griffith was able to get live S-strain bacteria from the blood of deceased mice.
4. Griffith obtained live S-strain bacteria from the blood of the dead mice.
5. He came to the conclusion that the live R-strain bacteria must have picked up something (which he named the ransforming principle) from the heat-killed S-bacteria and became S-type. R-type bacteria were able to synthesise capsules thanks to the transforming principle, and they became pathogenic.
6. Thus, F. Griffith first demonstrated genetic transformation.