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Genes
Gregor Mendel concluded from his experiments with pea plants that an organism’s characteristics are inherited in discrete “packages” which became known as genes. -
DNA first discovered
DNA was first discovered by the Swiss scientist Friedrich Miescher when he isolated it (along with RNA) from human white blood cells. -
Chromosomes first seen
Chromosomes were first seen under the microscope. Chromosomes contain protein as well as DNA and it was assumed that the proteins carried the genes since their molecular structure was much more complex. -
DNA structure
It was concluded that DNA consisted of 3 types of chemicals: sugars, phosphates and bases of which there were four types -
Connection between DNA and genetic structure
A series of experiments by Oswald Avery, Colin MacLeod and Maclyn McCarty showed that it was indeed DNA that was the genetic material of the cell. -
First clue to the molecule's structure
Erwin Chargoff discovered that the amount of adenine in a sample of DNA was always the same as the amount of thymine, and the amount of cytosine was always the same as the amount of guanine. This was an important “clue” to the molecule’s structure. -
The use of X-ray crystallography
Rosalind Franklin and Maurice Wilkins were using a new technique called X-ray crystallography to work out the shape of the molecule. Franklin found that DNA is a long molecule of regularly repeating units that are arranged in a helical shape. Watson and Crick experimented with various 2 and 3 helical structures without success. One of their unsuccessful models was based on inaccurate remembrances of one of Franklin’s lectures. -
Photograph 51
Wilkins showed them Franklin’s famous “Photograph 51” (without Franklin’s permission), Watson and Crick hit on a double helical model of DNA which is the currently accepted model today.
Not only does the model explain how information is coded, it also shows how DNA can be easily copied during cell division. -
Nobel prizes
Watson, Crick and Wilkins received the Nobel prize in Physiology or Medicine, without giving Frankin credit
