3. History Now that you know what DNA is and how it is constructed, how do you think it was found? Chargaff’s Rule: One of the puzzling facts about DNA was a curious relationship between its nucleotides. Erwin Chargaff (an American biochemist) had discovered that the percentages of guanine and cytosine bases are almost always equal in any sample of DNA.

5. X-Ray Evidence: In the early 1950’s a British scientist named Rosalind Franklin began to study DNA. Just like anyone else that is curious Rosalind wanted to see what she was studying, so she literally took a picture of DNA with an X-ray. Unfortunately she was not recognized for her work and discovery until after she passed away. She developed radiation poisoning from working with the x-rays. Watson and Crick were the two recognized for the discovery of the shape of DNA, then later Franklin was added to the discovery.

6. The Double Helix: At the same time that Franklin was continuing her research, Francis Crick and James Watson were trying to build a three-dimensional model of the molecule. Watson and Crick used Rosalind’s picture to figure out DNA’s puzzle and solved what is known as the double helix.