Describe the experiment performed by Griffith. What conclusions did he infer from his observations?
Solution
Griffith performed the experiment on bacterial cells to study the process of transformation. It is the process in which naked DNA of one bacterial cell is transferred into another bacterial cell.
For his experiment, he selected two strains of bacteria Diplococcus pneumoniae. One strain was S-train which had a mucous coat on its surface and was virulent. The other strain was the R- strain, which had no mucous coating and was a virulent
Griffith conducted a series of the experiment.
1) He first injected mice with S-strain, the mice died due to pneumonia.
2) Then he injected other mice with R-strain, the mice survived.
3) Now, Griffith injected mice with heat-killed S-strain, the mice survived
4) Next, he injected the mice with a mixture of heat-killed S-strain and live R-strain. The mice died because of pneumonia. He isolated live S-strain from the dead mice.
Griffith concluded that, once DNA is taken up by the recipient cell (R-strain), recombination occurred. A bacterium that has inherited the DNA of the donor is said to be transformed.
