NEET Botany Molecular Basis of Inheritance Questions Solved


Frederich Griffith claimed that R-strain Streptococcus pneumoniae had been transformed by heat killed 

S-strain bacteria. Explain the findings.

Transformation was first studied by Frederick Griffith in 1928. He conducted experiments

with streptococcus pneumoniae, the bacterium responsible for pneumonia.

1. He observed two strains of this bacterium, some produce shiny colonies (S) 

while others produce rough colonies (R). Strain bacteria have a mucous (polysaccharide)

coat, while R-strain does not have.

2. The S-strain bacteria are virulent while the R-strain bacteria are non-virulent.

3. When live S-type bacteria were injected into mice, they died from pneumonia.

                S-straininject into micemice die

4. Mice injected with the R-strains, mice survived.

              R-straininject into micemice live 

5. Heat killed S-strain bacteria were injected into mice, did not kill them.

              S-straininject into micemice live(heat killed)

6. S-strain (heat killed) were mixed with R-strain (live) and then injected into 

mice, the mice died of puneumonia.

             S-strain(heat killed)      +                    inject into micemice dieR-strain (live)

7. He isolated living S bacterium from the dead mice. He concluded that the R-strain 

bacteria had somehow been transformed by the heat killed S-strain bacteria. Some 

transforming principle transferred from the heat killed S-strain bacteria. It changed

the R-bacteria into S-bacteria, so R-bacteria were able to produce a smooth polysaccharide

coat and became virulent.

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