Appendix A: Key Milestones in Genetics and Molecular Biology Timeline

1859 Natural Selection

Charles Darwin wrote “On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life.

The Origin of Species Title Page (1859)tio

1865 Heredity Transmitted in Units

Gregor Mendel’s experiments on peas demonstrate that heredity is transmitted in discrete units. The understanding that genes remain distinct entities even if the characteristics of parents appear to blend in their children.

Characteristics of Pea Plants Gregor Mendel Used in Inheritance Experiments

1869 DNA Isolated

Frederick Miescher isolates DNA from cells for the first time and calls it “nuclein.”

A Portrait of Friedrich Miescher (1844–1895)

1879 Mitosis is Described

Walter Flemming describes chromosome behavior during animal cell division. He stains chromosomes to observe them clearly and describes the whole process of mitosis in 1882.

A Portrait of Walther Flemming (1843–1905)

1902 Chromosome Theory of Inheritance

Walter Sutton observes that the segregation of chromosomes during meiosis matched the segregation pattern observed by Mendel.

A portrait of Walter S. Sutton (1877–1916)

1909 The Word “Gene” is Coined

Wilhelm Johannsen coins the word “gene” to describe the Mendelian unit of heredity. He also uses the terms genotype and phenotype to differentiate between the genetic traits of an individual and its outward appearance.

A Portrait of Wilhelm Johannsen (1857–1927) Danish Biologist

1911 Chromosomes Carry Genes

Thomas Hunt Morgan and his students study fruit fly chromosomes. They show that chromosomes carry genes and discover genetic linkage.

Drosophilia Gene Linkage Map

George Beadle and Edward Tatum’s experiments on the red bread mold, Neurospora crassa, show that genes act by regulating distinct chemical events. They propose that each gene directs the formation of one enzyme.

Neurospora Crassahyphae

1952 Genes are made of DNA

Alfred Hershey & Martha Chase show that only the DNA of a virus needs to enter a bacterium to infect it, providing strong support for the idea that genes are made of DNA.

Scientists Alfred Hershey (1908–1997) and Martha Chase (1927–2003)

1953 Double Helix

Francis H. Crick and James D. Watson described the double helix structure of DNA. They received the Nobel Prize for their work in 1962.

DNA animation


Media Attributions

  • 1859 Natural Selection: The Origin of Species Title Page, from John Murray (Publisher), via Wikimedia Commons. [public domain]
  • 1865 Heredity Transmitted in Units: File:Gregor Mendel – characteristics of pea plants – english, by Sciencia58 [username], viaWikimedia Commons. [Original image by LadyofHats.] CC0
  • 1869 DNA Isolated: Friedrich Miescher (scientist), by unknown artist, copied from , via Wikimedia Commons. [public domain]
  • 1879 Mitosis is Described: Walther Flemming (1843 – 1905), by unknown author, Original source:, via Wikimedia Commons. [public domain]
  • 1902 Chromosome Theory of Inheritance: A portrait of Walter S. Sutton taken prior to 1916; Original source from, via Wikimedia Commons. [public domain]
  • 1909 The Word “Gene” is Coined: Wilhelm Johannsen (1857-1927) Danish biologist, by unknown author, The History of Biology de Erik Nordenskiöld, Ed. Knopf, 1928, via Wikimedia Commons. [public domain]
  • 1911 Chromosomes Carry Genes:
    • Drosophilia Gene Linkage Map by Twaanders17, via Wikimedia Commons. CC BY-SA 4.0
    • Neurospora crassahyphae by Roland Gromes, via Wikimedia Commons. CC BY-SA 3.0
  • 1941 One Gene, One Enzyme Hypothesis: Scientists Alfred Hershey and Martha Chase, photograph by Rohit Kumar Sengupta, via Wikimedia Commons. CC BY-SA 4.0
  • 1952 Genes are made of DNA: Scientists Alfred Hershey (1908–1997) and Martha Chase (1927–2003)
  • 1953 Double Helix: DNA animation [gif] by brian0918 [username], via Wikimedia Commons. [public domain]


A&E Television Networks. (2009, November 24). James D. Watson and Francis H.C. Crick (image). Chemical structure of DNA discovered.

Murray, J. [publisher]. (2022, March 11). File:Origin of Species title page.jpg. Wikimedia Commons.

Ruiz Villarreal, M. [user: ladyofhats]. (2018, October 9). File:Gregor Mendel – characteristics of pea plants – english [digital image – reworked by user: Sciencia58]. Wikimedia Commons.

Wikipedia contributors. (2017, June 9). File:Friedrich Miescher.jpg.  Wikimedia Commons.

Wikipedia contributors. (2021, February 16). Thomas Hunt Morgan. Wikipedia.

Wikipedia contributors. (2014, October 30). File:Walter sutton.jpg. Wikimedia Commons.

Wikipedia contributors. (2020, August 12). File:Walther flemming 2.jpg. Wikimedia Commons.

Wikipedia contributors. (2020, December 10). Wilhelm Johannsen. Wikipedia.



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Open Genetics by Natasha Ramroop Singh, Thompson Rivers University is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

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