Griffith's experiment

Diagram of Griffith's Experiment

Griffith's Experiment, conducted by Frederick Griffith in 1928, was a pivotal study in the field of genetics that demonstrated the phenomenon of bacterial transformation. This experiment provided the first indication that DNA could be the molecule responsible for heredity.

Background

In the early 20th century, the nature of the genetic material was unknown. Scientists were debating whether proteins or nucleic acids were the carriers of genetic information. Griffith's work with Streptococcus pneumoniae, a bacterium that causes pneumonia, was instrumental in shifting the focus towards nucleic acids.

The Experiment

Griffith used two strains of Streptococcus pneumoniae: the S strain, which was virulent and had a smooth appearance due to its polysaccharide capsule, and the R strain, which was non-virulent and had a rough appearance.

Procedure

Griffith conducted a series of experiments on mice:

• Injection of S strain: Mice injected with the live S strain developed pneumonia and died.
• Injection of R strain: Mice injected with the live R strain remained healthy.
• Injection of heat-killed S strain: Mice injected with heat-killed S strain remained healthy.
• Injection of R strain and heat-killed S strain: Mice injected with a mixture of live R strain and heat-killed S strain developed pneumonia and died.

Results

The surprising result was that the non-virulent R strain had been "transformed" into a virulent form by some "transforming principle" from the heat-killed S strain. This suggested that the genetic information from the dead S strain was taken up by the live R strain, enabling it to produce a capsule and become virulent.

Significance

Griffith's Experiment was significant because it suggested that the "transforming principle" was a molecule that could transfer genetic information. This laid the groundwork for later experiments by Oswald Avery, Colin MacLeod, and Maclyn McCarty, who identified DNA as the "transforming principle."

Related Pages

• Oswald Avery
• DNA
• Bacterial transformation
• Streptococcus pneumoniae