1. Who: Frederick Griffith When: 1928  What did they do: Experimented with mice using 2 strains of pneumonia bacteria (one harmful and one harmless)  He killed the harmful strain by heating it and mixed it with the harmless strain;  Harmless bacteria “transformed” into harmful bacteria & killed mice

2. Who: Oswald Avery (and McCarty & MacLeod) When: 1944 What did they do:  Repeated Griffith’s experiments  Wanted to find the “transforming factor”, (Is it the protein or the DNA?)  Protein + DNA = Transformed DNA + no Protein = Transformed DNA + no Protein = Transformed Protein + no DNA = Not transformed Protein + no DNA = Not transformed  Realized DNA is the transformation factor.

3. Who: Erwin Chargaff When: 1950 What did he do:  Found that the bases adenine and thymine always pair together and cytosine and guanine always pair together  Chargaffs Rule:  A pairs with T  C pairs with G

4. Who: Rosalind Franklin and Maurice Wilkins When: 1951 What did they do:  Used x-ray crystallography to take pictures of DNA and discovered the shape (double stranded and twisted like a helix)

5. Who: Alfred Hershey and Martha Chase When: 1952 What did they do:  Conducted “Blender experiment” with 2 sets of bacteriophages  Proved that genes are made up of the nucleic acid DNA  Concluded that DNA must be the genetic material

6. Who: James Watson and Francis Crick When: 1953 What did they do:  Took all the information that the other scientists gathered and put together the first complete model of DNA  Won the Nobel Prize for this accomplishment