Final answer:
Frederick Griffith used two types of Streptococcus pneumoniae, the non-pathogenic R strain and the pathogenic S strain, in his experiments. Injecting mice with live S strain caused death, while the non-lethal R strain and heat-killed S strain did not. When mice were injected with both live R strain and heat-killed S strain, the mice died, indicating a transformation to a pathogenic strain.
Step-by-step explanation:
Griffith's Transformation Experiments with Strep pneumoniae
In his groundbreaking experiments, Frederick Griffith used two types of Streptococcus pneumoniae to inject into mice, which are commonly known as R strain and S strain. The R strain, or rough strain, was non-pathogenic and did not cause harm to the mice. In contrast, the S strain, or smooth strain, was pathogenic and lethal. Griffith's key findings involved four different scenarios:
- Injecting mice with live S strain led to deadly pneumonia
- Injecting mice with live R strain caused no illness
- Injecting mice with heat-killed S strain resulted in no harm
- Injecting mice with a mixture of live R strain and heat-killed S strain surprisingly caused death, and live S strain bacteria were recovered, indicating a transformation had occurred
This experiment showed that some 'transforming principle' from the heat-killed S strain was taken up by the R strain, converting it into a pathogenic form. Griffith's transformation experiments laid the groundwork for understanding DNA as the genetic material.