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  • (a) Explain the Griffith's 'transformation principle' experiment. (b) In the above experiment. "heat which is killed one type of bacteria, did not destory the properties of genetic material". Justify.  

(a) Explain the Griffith's 'transformation principle' experiment.

(b) In the above experiment. "heat which is killed one type of bacteria, did not destory the properties of genetic material". Justify.

 

 

 

 
 
 
 
 

Answers (1)

a) When Streptococcus pneumoniae (pneumococcus) bacteria are grown on a culture plate, some produce smooth shiny colonies (S) while others produce rough colonies (R). This is because the S strain bacteria have a mucous (polysaccharide) coat, while R strain does not. Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia.

Griffith was able to kill bacteria by heating them. He observed that heat-killed S strain bacteria injected into mice did not kill them. When he injected a mixture of heat-killed S and live R bacteria, the mice died. Moreover, he recovered living S bacteria from the dead mice.

b) Griffith 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, had enabled the R strain to synthesise a smooth polysaccharide coat and become virulent. This must be due to the transfer of the genetic material. However, the biochemical nature of genetic material was not defined from his experiments.

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Priyanka Kumari

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