Griffith experiment

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In 1928 Frederick Griffith conducted an experiment which advocated for the ability of bacterial cells to transfer genetic information from one to another, in a process called transformation. He utilised two strains (S and R) of Streptococcus pneumoniae which grow on solid mediums to form colonies of bacteria. The S type of S. pneumoniae synthesised a gelatinous capsule composed of complex carbohydrates which would protect the bacteria against the immune system of another organism, thus the bacteria caused pneumonia. The formation of the capsules also allowed for large colonies with smooth exteriors. On the other hand, the R type did not synthesis a capsule and so would be killed by the immune system of the organism it infects. In this experiment, three sets of mice were investigated. The first had only the S strain injected, the second had only the R strain and the third had both living R strains and heat-killed S strains. The first group contracted pneumonia whilst the second did not, as expected. The third group of mice however also contracted pneumonia and therefore died. To further investigate these results, blood from the dead mice of the third group was examined and the bacteria were found to have produced S cultures with live S colonies even tho the injected strain had been killed. This suggested that the injected material from the dead S cells included a substance that can be transferred into living R cells that then enables them to synthesize the S type capsule. Therefore showing that the R strain undergo transformation into the S strain, furthermore the ability to synthesize the capsule was inherited by the progeny of the transformed bacterian[1].


  1. Genetics : analysis of genes and genomes, Daniel L. Hartl and Maryellen Ruvolo, 8th Edition, Burlington, MA : Jones and Bartlett Learning, 2012.
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