Frederick Griffith’s experiments in 1928 were pivotal in establishing the concept of DNA as the carrier of genetic information. His work primarily involved two strains of the bacterium Streptococcus pneumoniae: the virulent smooth strain (S) and the non-virulent rough strain (R).
Griffith’s Experiment
Griffith conducted a series of injections in mice to observe the effects of these bacterial strains:
- Injection of S Strain: Mice injected with live S strain bacteria developed pneumonia and died.
- Injection of R Strain: Mice injected with live R strain bacteria remained healthy.
- Injection of Heat-Killed S Strain: Mice injected with heat-killed S strain bacteria also survived, indicating that the heat treatment had rendered the bacteria non-virulent.
- Injection of Mixture: The critical experiment involved mixing heat-killed S strain with live R strain bacteria. Mice injected with this mixture died, and upon examination, both live S and R strains were found in the blood of the deceased mice.
Conclusion: The Transforming Principle
From these observations, Griffith concluded that some “transforming principle” from the dead S strain bacteria had transformed the live R strain into a virulent form. This was the first evidence suggesting that genetic information could be transferred between bacteria, laying the groundwork for future discoveries regarding DNA.
Subsequent Research
Griffith’s findings prompted further investigations into the nature of the transforming principle. In 1944, Oswald Avery, Colin MacLeod, and Maclyn McCarty conducted experiments that identified DNA as the substance responsible for this transformation. They demonstrated that the transformation could be inhibited by enzymes that degrade DNA, confirming that DNA, not proteins, was the genetic material.
Impact on Genetics
Griffith’s experiment was crucial in shifting the scientific consensus towards DNA as the hereditary material. It opened avenues for molecular biology and genetics, influencing subsequent research that ultimately led to the discovery of DNA’s structure by Watson and Crick in 1953. Thus, Griffith’s work not only established the concept of transformation in bacteria but also set the stage for understanding DNA’s role in heredity and genetic information transfer