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Albrecht Kossel was a German biochemist that analyzed the makeup of nuclein. He identified it as a nucleic acid and changed its name to deoxyribonucleic acid (DNA). In addition, Kossel later isolated the bases (adenine, cytosine, guanine, thymine, and uracil).

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Johann Friedrich Miescher started an investigation to discover the key components of white blood cells. In the process he discovered that when he added acid to a solution of the cells, a substance separated. Miescher called this mysterious nuclein and it was the first time that DNA was isolated.

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Walter Flemming stains chromosomes with dyes and observes their behavior during animal cell division. He introduces the term chromatin as well as the name of the process mitosis.

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Mendel's discoveries about inheritance with pea plant breeding experiments resurfaced in the early 1900s.

Scientists Walter Sutton (studying grasshopper chromosomes) and Theodor Boveri (studying roundworm embryos) were both working individually with genetics. However, they were both they both came to the same conclusion and were the first to present the idea that chromosomes were the ones responsible for passing down genetic material from parent to offspring. These conclusions explained the results of Mendel's experiments.

It wasn't until 1902 that Edmund Beecher Wilson united their work and published the Boveri-Sutton chromosome theory of heredity.

In 1915, Thomas Hunt Morgan experimented with fruit fly Drosophila melanogaster confirming the theory previously established.

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Frederick Griffith conducted a series of experiments with a bacteria called Streptococcus. He noticed two strains (genetic variants), a smooth virulent (lethal to mice) termed S strain, and a non-virulent rough one termed R strain.

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His most prominent experiment involved ejecting both strains of bacteria to mice. Of course, some died, but he noticed live virulent bacteria in their blood. This was termed "transformation" where genetic information was transferred from the dead virulent S strain to the live non-virulent R strain.

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Griffith came to the conclusion that the R-strain bacteria must have absorbed a "transforming principle" from the heat-killed S bacteria, allowing them to "transform" into smooth-coated bacteria and become virulent.

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1944 Avery, MacLeod, and McCarty's Experiment

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1944 Avery, MacLeod, and McCarty's Experiment

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Oswald Avery, Colin MacLeod, and Maclyn McCarty wanted to determine which component of the virulent bacteria was responsible for the transformation in Griffith's work. They treated it with enzymes that destroyed various biomolecules (proteins, lipids, RNA, and DNA) and tested each sample for its ability to transform non-virulent bacteria. They found that the sample treated with the enzyme that destroyed DNA was unable to cause transformation, thus proving that DNA's responsible for carrying genetic information.

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Rosalind Franklin takes the famous ‘Photo 51’, a highly detailed image of the ‘B’ or hydrated form of DNA. This reveals helical shape of DNA.

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1952: Hershey & Chase's Blender Experiment

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1952: Hershey & Chase's Blender Experiment

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Martha Chase and Alfred Hershey's experiment involved the T2 bacteriophage, a virus that infects bacteria. Their goal was to determine whether the genetic material of the virus was DNA or protein.
They labeled the DNA with radioactive phosphorus-32 and protein coat with radioactive sulfur-35. Then they infected Escherichia coli bacteria (type that lives in intestines).
They observed that only the radioactive phosphorus (DNA) entered the bacterial cells, and the sulfur (protein) remained outside. This indicated that DNA was the genetic material that the virus transmitted to the bacterial cells.

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James Watson (who had previously looked at the photo 51 without Franklin's knowledge) and Francis Crick propose a model for the structure of the DNA molecule (helix).

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Crick proposes that the DNA sequence is translated into proteins using RNA

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The first rapid DNA sequencing method is designed by Frederick Sanger. This is later used for decades to sequence genes and genomes of countless organisms.

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Christiansen, T. (2021, April 15). Interactive timeline: 150 Years of DNA | OpenMind. BBVA Openmind. Retrieved August 22, 2023, from https://www.bbvaopenmind.com/en/science/bioscience/history-dna-timeline/

The discovery of DNA – YourGenome. (2021, July 21). YourGenome. Retrieved August 22, 2023, from https://www.yourgenome.org/stories/the-discovery-of-dna/

Nightingale, K. (2020, April 10). DNA: a timeline of discoveries. BBC Science Focus. Retrieved August 22, 2023, from https://www.sciencefocus.com/the-human-body/dna-a-timeline-of-discoveries

1.2: DNA is the Genetic Material. (2016, May 27). Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Genetics/Online_Open_Genetics_(Nickle_and_Barrette-Ng)/01%3A_Overview_DNA_and_Genes/1.02%3A_DNA_is_the_Genetic_Material#:~:text=of%20the%20bacteria.-,Hershey%20and%20Chase's%20Experiment%20(1952),4).

Admin. (2017, October 30). The Hershey and Chase Experiments : DNA as the Genetic Material. BYJUS; BYJU’S. https://byjus.com/biology/dna-genetic-material/#:~:text=In%201952%2C%20Alfred%20Hershey%20and,for%20Hershey%20and%20Chase%20experiment.

Avery, O. T., MacLeod, C. M., & McCarty, M. (1944). Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated from Pneumococcus Type III. Journal of Experimental Medicine, 79(2), 137-158.

DNA as a Genetic Material | Biology. (2016, October 20). Biology Discussion. https://www.biologydiscussion.com/genetics/dna-as-a-genetic-material-biology/56216

Khan Academy. (2023). Khanacademy.org. https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-discovery-and-structure/a/classic-experiments-dna-as-the-genetic-material