1.2: DNA is the Genetic Material
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Microbiologists identified two strains of the bacterium Streptococcus pneumoniae . The R-strain produced rough colonies on a bacterial plate, while the other S-strain was smooth (Figure \(\PageIndex{2}\)). More importantly, the S-strain bacteria caused fatal infections when injected into mice, while the R-strain did not (top, Figure \(\PageIndex{3}\)). Neither did “heat-treated” S-strain cells. Griffith in 1929 noticed that upon mixing “heat-treated” S-strain cells together with some R-type bacteria (neither should kill the mice), the mice died and there were S-strain, pathogenic cells recoverable. Thus, some non-living component from the S-type strains contained genetic information that could be transferred to and transform the living R-type strain cells into S-type cells.