Circa 3000 BC
Ancient Chinese and Sumerian farming techniques selectively breed crops and animals.

1866
Gregory Mendel publishes his work on the heredity of peas, in which he notes certain factors, later called genes, are passed from parent to offspring.

1869
Working with soiled bandages, Friedrich Miescher identifies DNA as an acidic substance in cell nuclei. It is at first called "nuclein."

1900
Hugo deVries, Carl Correns, and Eric von Tschermak independently confirm Mendel’s work.

1911
Thomas Hunt Morgan shows that genes are located linearly along chromosomes.

1928
In an experiment with lab mice, Frederick Griffith transfers the deadly component of a strain of pneumonia bacteria to an innocuous bacteria strain,

1929
Phoebus Levene discovers that the sugar deoxyribose is present in nucleic acids and later shows that DNA is made up of nucleotides, which are made up of a deoxyribose sugar, a phosphate group, and one of four bases.

1943
William Astbury takes first X-ray diffraction images of DNA.

1944
Oswald Avery, Colin MacLeod, and Maclyn McCarty show that DNA, and not protein, is the "transforming factor" Griffith first identified.