Molecular Biology Chronology 1869 Swiss Chemist Johann Friedrich Miescher first isolated DNA from salmon egg 1920’s Robert Feulgen developed a DNA specific dye showing DNA located in the nucleus, particularly in chromosomes Chronology 1928 Fred Griffith, a British microbiologist was the first to demonstrate the transformation of a genetic trait. Transformation of non virulent, unencapsulated diplococcus pneumonia bacteria to a virulent, encapsulated form Chronology 1944 Oswald Avery American microbiologist was able to demonstrate that Griffith’s transformation factor was DNA and not protein. Chronology 1952 - Alfred Hershey and Martha Chase, American microbiologists were able to demonstrate that only DNA was transferred from bacteriophages to infected bacterial cells. Chronology 1951 Erwin Chargraff demonstrated that the bases in DNA were found in strict ratios Purine bases = pyrimidine bases A = T and G = C Chronology 1953 James Watson (American) and Francis Crick (British Physicist) working at Cambridge University in England demonstrated that the structure of DNA was a double helix, ahead of Rosalind Franklin and Maurice Wilkins (Oxford) and Linus Pauling (U of California) Chronology 1961 M. Nirenberg and H. Matthaei identified components necessary for DNA replication. In a control using poly U they found a polymer of phenylalanine was produced, showing the first codon, UUU.