Question

Explain the experiment that made Frederick Griffith to conclude that R strain of Streptococcus pneumoniae somehow been transformed by heat killed S strain.

Accepted Answer

Griffith cultured Streptococcus pneumoniae, which grew in two ways during the experiment. The smooth colonies (S) were on one culture plate, while the rough colonies (R) were on the other.
Griffith conducted an experiment in which he injected both S and R strains into mice and discovered that the principle of transformation exists.

Those who were infected with the S strain developed pneumonia and died, whereas those who were infected with the R strain survived.

Griffith heat-killed the S strain bacteria and injected it into mice in the second stage, but the mice survived.

The heat-killed S strains were then combined with live R strains. This mixture was administered into the mice, and they died.

He also observed live S strain bacteria in dead mice

Based on his observations, Griffith came to the conclusion that R strain bacteria had been altered by S strain bacteria. The R strain inherited a virulent-building 'transforming principle' from heat-killed S strain bacteria. And he identified genetic material as the transformative principle.

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