The First demonstration of bacterial transformation.An
"S" or SMOOTH coat strain, which is lethal to mice.
An "R" or rough strain, which will not hurt the mouse.
Griffith found that he could heat inactivate the smooth strain.
However, if he were to take a mixture of the heat-inactivated S strain,
mixed with the R strain, the bacteria would die. Thus there was
some Material in the heat-killed S strain that was responsible
for "transforming" the R strain into a lethal form.
Fred Griffith (and a lab co-worker) was killed in their
laboratory in 1940 from a German bomb. However, their work continued on in
the U.S., and in 1944, Oswald Avery, C.M. MacLeod, and M. McCarty carefully
demonstrated that the ONLY material that was responsible for the transformation
was DNA - thus, DNA was the "Genetic material" - however, many
scientists were still not sure that it was REALLY DNA (and not proteins) that
was the genetic material.
Experiments done by Frederick Griffith (in London) in 1928 found there were two
different types of the bacterium Streptococcus pneumoniae:
In 1952, Alfred Hershey and Martha Chase (she was an UNDERGRADUATE at the
time!) demonstrated clearly that DNA must be the genetic material, using