A method is described for teaching the analysis of X-ray diffraction of DNA through a series of steps utilizing the original methods used by James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin. The X-ray diffraction pattern led to the conclusion of the basic helical structure of DNA and its dimensions while basic chemical principles led to verify the structure along with the counter-oriented nature of the two helices, the hydrogen bonding between purines (adenine and guanine) and pyrimidines (thymine and cytosine), and the implications to gene replication.