History of DNA

Gregor Mendel

Gregor Mendel, who was a monk, played a very important role in the discovery of genes and heredity. He is considered to be “the father of genetics” with his famous experiment about peapods that explained the patterns of inheritance. Because I could go on and on about Mendel’s experiment, I will try to sum it up in a nutshell:

Mendel originally hypothesized that in every generation, a plant inherits two “units of information” (they were called units at that time because genes had not yet been established) for a trait, one from each parent. He crossed-fertilized two true-breeding pea plants, one with purple flowers and one with white flowers, and observed the offspring’s characteristics, they both had purple flowers. Then he let the offspring self-fertilize, and he saw that some flowers were white but mainly they were still purple. He continued to let the pea plants self-fertilize and he eventually saw that his hypothesis was correct. Both “units of information” from each parent flower existed, and one trait was dominant (the purple) because it covered the other trait (the white)

Though this is very far from what DNA actually is, without this information about inheritance, the idea of heredity would never have developed and without the idea of heredity, nobody would know about DNA.

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Frederick Griffith

In his first experiment, he injected the live R bacteria cells into the mice and the mice lived.

In his second experiment, he injected the live S bacteria cells into the mice and mice died.

In his third experiment, he killed the harmful S cells with extreme heat, and then injected the dead S cells into the mice and the mice lived.

In his last experiment, he added live R cell (which are harmless) to the already dead heat-killed S cells, and then injected it into the mice, but the mice died!

Griffith found from this experiment that even though he had killed the S cells, he hadn’t destroyed their hereditary material, which was the one part that caused the disease! When some more experiments had been done, it had been discovered that the harmless R cells, had used the information from the hereditary material of the dead S cells and became harmful; this he called, hereditary transformation.

(Oh and by the way… he never did find the vaccine.)

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Oswald Avery

In 1944, they had reported that DNA, not proteins (which was believed at the time), was the hereditary substance in these extracts. They backed there report up by the results of an experiment in which they added protein-digesting enzymes to some of the extracts, and the cells were still transformed, but when the added an enzyme that broke the DNA but not the protein, the hereditary transformation was blocked.

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Erwin Chargaff

Erwin Chargaff was a biochemist who first figured out the equation for the different bases. Here is what he concluded: the amount of (A)denine will always equal the amount of (T)hymine and the amount of (G)uanine will always equal the amount of (C)ytosine.

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Maurice Wilkins and Rosalind Franklin

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James Watson and Francis Crick

In 1951 James Watson and Francis Crick began to examine the DNA’s structure. Using previous X-ray diffraction photos of DNA fibers taken by Maurice Wilkins and Rosalind Franklin, they discovered that it showed an X shape... which is also the characteristic of a helix. In April of 1953, using this information, they came up with the double helix, the structure that is almost always associated with DNA.

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