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!

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.

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

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

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.

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

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!

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