Answer :
Griffith's experiment, conducted in 1928 by Frederick Griffith, demonstrated that genetic material could indeed be transferred between different strains of bacteria. The process observed in his experiment is now known as "Bacterial transformation".
Here's a step-by-step explanation of the experiment and its significance:
Who and What: Frederick Griffith was a British bacteriologist who was studying Streptococcus pneumoniae, a bacterium that causes pneumonia.
The Experiment Setup: Griffith worked with two strains of this bacterium:
- The S strain: Has a smooth appearance due to a protective polysaccharide capsule and is virulent, meaning it can cause disease.
- The R strain: Lacks the capsule, appearing rough, and is non-virulent.
Experiment Methodology:
- Griffith injected mice with the S strain and they developed pneumonia and died.
- Mice injected with the R strain survived.
- He then injected mice with heat-killed S strain bacteria; these mice also survived, indicating that the heat-killed bacteria were not harmful.
- Finally, he injected mice with a mixture of heat-killed S strain and live R strain bacteria. Interestingly, these mice developed pneumonia and died.
Discovery: Griffith found that live, virulent S strain bacteria could be isolated from these dead mice. This indicated that some "transforming principle" from the dead S strain bacteria had transformed the R strain into the virulent S strain.
Significance: This transformation suggested that genetic information could be transferred and led to the discovery of DNA as the material responsible for heredity. This experiment laid the groundwork for future research by scientists like Oswald Avery, who further identified DNA as the "transforming principle.”
Conclusion: The process in which genetic material was transferred from the heat-killed S strain to the R strain, enabling it to express new, virulent traits, is called "Bacterial transformation," which is the correct answer (D) among the given options.
