1869 DNA (first called "nuclein") is identified by Friedrich Miescher as an acidic substance found in cell nuclei. The significance of DNA is not appreciated for over 70 years.
1900 Mendel's experiments from 1866 are "rediscovered" and confirmed by three separate researchers (one Dutch, one German, one Austrian). A British man (William Bateson) soon translates Mendel's paper into English and champions the study of heredity in England.
1902 A human disease is first attributed to genetic causes ("inborn errors of metabolism"). (Sir Archibald Garrod, alkaptonuria)
1902 The chromosome theory of heredity is proposed by Sutton. Boveri recognizes that individual chromosomes are different from one another, but he doesn't make a connection to Mendelian principles. Nevertheless, Boveri is given co-credit by friend E.B. Wilson (Sutton's supervisor) for proposing the chromosome theory of inheritance.
1905 The word "genetics" is coined by William Bateson.
1905 Some genes are linked and do not show independent assortment, as seen by Bateson and Punnett.
1903-9 First experiments on quantitative traits in broad beans by Wilhelm Johanssen and in wheat by Herman Nilsson-Ehle.
1910-11 The chromosome theory of heredity is confirmed in studies of fly eye color inheritance by T.H. Morgan and colleagues.
1913 First ever linkage map created by Columbia undergraduate Alfred Sturtevant (working with T.H. Morgan).
1910's-30's The eugenics movement is popular, fueling racist sentiment and leading to involuntary sterilization laws.
1925-27 H. Muller shows that X-rays induce mutations in a dose-dependent fashion.
1928 Some component of heat-killed virulent bacteria can "transform" a non-virulent strain to become virulent, as shown by Fred Griffith. This sets the stage for work done in 1944.
1931