Final answer:
The bacterium used by F. Griffith in the transformation experiment was Streptococcus pneumoniae. By injecting a mixture of live R strain and heat-killed S strain, Griffith discovered that something from the S strain transformed the R strain into the pathogenic S strain.
Step-by-step explanation:
The bacterium that was used by F. Griffith in the transformation experiment that signaled the beginning of the discovery of the genetic material was Streptococcus pneumoniae.
Griffith conducted his experiments with two strains of S. pneumoniae - the rough (R) strain and the smooth (S) strain. The R strain is nonpathogenic and lacks a capsule, while the S strain is pathogenic and has a capsule.
In his experiment, Griffith injected a mixture of live R strain and heat-killed S strain into mice. To his surprise, the mice died and the isolated bacteria from the dead mouse were only the S strain. This led Griffith to conclude that something had passed from the heat-killed S strain to the live R strain and transformed it into the pathogenic S strain.