3. 3000 BC Evidence of selective breeding in crops and animals from ancient Chinese and Sumerian farmers 1866 Gregor Mendel publishes his work on peas and heredity 1869 Friedrich Miescher discovers the acidic substance in the nucleus of all cells; calls it “nuclein” NUCLEIC ACID

4. 1928 Frederick Griffith fails at making a vaccine for pneumonia; discovers “Transformation Principle”

5. 1928 Frederick Griffith fails at making a vaccine for pneumonia 1929 Phoebus Levene discovers structures present in DNA: deoxyribose sugar, phosphate groups, and one of four bases (A,T,G,C)

6. 1928 Frederick Griffith fails at making a vaccine for pneumonia 1929 Phoebus Levene discovers structures present in DNA: deoxyribose sugar, phosphate groups, and one of four bases (A,T,G,C) 1944 Oswald Avery, Colin MacLeod, and Maclyn McCarty show that DNA, and not protein, is the "transforming factor" Griffith first identified.

7. 1950 Erwin Chargaff discovers ratio of bases; A=T, G=C “Chargaff’s Rule”

8. 1950 Erwin Chargaff discovers ratio of bases; A=T, G=C “Chargaff’s Rule” 1952 Maurice Wilkins and Rosalind Franklin take X-ray images of DNA crystals used by Watson and Crick 1953 James Watson and Francis Crick discover the structure of DNA

9. 1985 PCR developed 1989 First exoneration using DNA 1996 Dolly, the sheep; first mammal to be cloned 2003 Human Genome is sequenced

10. NUCLEOTIDE Bases Adenine = Thymine Cytosine = Guanine held together by hydrogen bonds Backbone Sugar phosphate ~10 base pairs per 360° turn

12. DNA is normally in chromatin state