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The Mona Lisa Molecule: Mysteries of DNA Unraveled


Karobi Moitra
Department of Biology
Trinity Washington University


This case study details the historical discovery of the structure of DNA. Images of this key molecule are as iconic as those of the Mona Lisa, and identifying its structure has proven to be as intriguing a mystery for scientists as the reason behind Mona Lisa's smile has been for art historians. The case is woven together by a series of fictional diary entries that detail the history of the discovery of DNA's structure, the major players involved, their ethical dilemmas, and the role of women in science. The case is designed for a high school course or introductory undergraduate genetics/ biochemistry courses. It can also be used as an interdisciplinary case study bridging genetics, bioethics, art, and the status of women in science. Designed as an interrupted case, it may be used in its entirety or in parts that pertain to a particular topic or discipline. No prior knowledge of genetics is required.


  • Accurately describe the chronology of events leading up to the discovery of DNA structure.
  • Describe the key features of DNA and how these features explain experimental data such as Chargaff's rules and Rosalind Franklin's X-ray crystallographic results.
  • Develop the skills to read and interpret scientific concepts from a primary research article.
  • Learn how to independently gather information from websites and apply that information to problem solving and critical thinking.
  • Explore the role of DNA in science, society, art, and literature.
  • Become aware of the ethical issues involved in scientific research.
  • Explore the role of women in science.


DNA; deoxyribonucleic acid; x-ray crystallography; model building; double helix; Rosalind Franklin; Francis Crick; James Watson; Cavendish; Hershey-Chase; Chargraff’s Laws; photo 51

Topical Areas

Ethics, History of science, Science and the media, Women in science

Educational Level

High school, Undergraduate lower division



Type / Methods

Analysis (Issues), Dilemma/Decision, Discussion, Interrupted, Journal Article



Subject Headings

Biology (General)  |   Genetics / Heredity  |   Biochemistry  |   Molecular Biology  |  

Date Posted


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The following video(s) are recommended for use in association with this case study.

  • The Double Helix hhmi/
    Short film that tells the story of the scientists and evidence involved in one of the most important scientific quests of the 20th century: the discovery of the structure of DNA. Running time: 16:53 min. Produced by HHMI BioInteractive. ec)
  • The Chemical Structure of DNA hhmi/
    Short animation showing the detailed structure of DNA. Running time: 2:44 mins. Produced by HHMI BioInteractive.
  • Chargaff's Ratio hhmi/
    Short animation that discusses Erwin Chargaff’s 1950 publication stating that in the DNA of any given species, the ratio of adenine to thymine is equal, as is the ratio of cytosine to guanine. This became known as Chargaff's ratio, and it was an important clue for solving the structure of DNA. Running time: 0;49 min. Produced by HHMI BioInteractive.


David Bird
Mount Royal University
Calgary Alberta Canada
A good case. I like the structure. It is ahistorical, (and not a little disrespectful) for the narrator to refer to Dr. Franklin as “Rosy.” This was not a nickname that she accepted—it was thrust on her by Watson in his own published version of the events in The Double Helix.

Karobi Moitra
Department of Biology
Trinity Washington University
Washington, DC
Author’s Reply: Thank you for your comments. It was not my intention to disrespect Rosalind Franklin in any way. The diary is written from the perspective of a fictional laboratory assistant; the diary itself is fictional but based on fact. The fact is that Watson did refer to Rosalind as “Rosy” in his book, The Double Helix. It is not known if she was aware of this nickname or not (or if she accepted it). Being the author of the case study I decided that my fictional character probably would have referred to Rosalind as “Rosy” simply because he was being mentored by Francis Crick and Francis might have referred to Rosalind by that nickname.