1. Mendel’s Experiments
Gregor Mendel was an Austrian monk who conducted experiments on pea plants
Mendel’s experiments answered many questions, but led to even more!
What are genes made of!
We will study Gregor Mendel in the next unit!

2. Griffith’s Experiment – 1928
Examined Streptococcus pneumoniae strains and mice
S strain of bacteria cause pneumonia
R strain of bacteria does NOT cause pneumonia
S strain of bacteria can be killed and rendered harmless by heating
R bacteria mixed with heat-killed S bacteria can still cause infection
Griffith's Experiment Video Clip
Completely unrelated experiment – trying to develop a vaccine against pneumonia
S strain is enclosed in a capsule that protects it from the body’s immune system making it virulent.

3. Griffith’s Experiment – 1928
Conclusion – Some type of material can move from the heat–killed S bacteria to the R bacteria to cause disease, and that this must be the genetic material—TRANSFORMATION
Transformation – change in the genotype (genetic makeup of an organism) caused when cells take up foreign genetic material
The cause of transformation was not known at the time

4. Griffith’s Experiment – 1928
The DNA of the heat–killed bacteria was not altered and became incorporated into the DNA of the live bacteria.
DNA can tolerate temperatures of 90˚C
Proteins are denatured ~ 60˚C

5. Avery’s Experiment – 1944
Material responsible for transformation is not affected by protein–destroying enzymes
The activity is stopped by a DNA–destroying enzyme!
Proved DNA is the material responsible for transformation.

6. Hersey and Chase’s Experiment – 1952
Worked with bacteriophages (viruses), which are made of only DNA and protein
Alternated between using radioactive DNA or radioactive protein
Sulfur isotope (35S) – only found in protein coat
Phosphorous isotope (32P) – only found in DNA
Looked to see if bacteria became radioactive when radioactive DNA or when radioactive protein was inserted by the virus
Hershey Chase Video Clip
Alfred Hershey and Martha Chase

7. Hersey and Chase’s Experiment – 1952
The bacteria only became radioactive when radioactive DNA was used
Conclusion – DNA is what is inserted into the bacteria, not the protein!

8. Hersey and Chase’s Experiment – 1952
They all prove that DNA, not proteins, are what is being passed on and is the heredity material!