DNA Day celebration, not an annual holiday. Every year from 2003 onward, annual DNA Day celebrations have been organized by the National Human Genome Research Institute (NHGRI), starting as early as April 23 in 2010, April 15 in 2011 and April 20 in 2012. April 25 has since been declared "International DNA Day" and "World DNA Day" by several groups. DNA Day National DNA Day is a holiday celebrated on April 25. It commemorates the day in 1953 when James Watson, Francis Crick, Maurice Wilkins, Rosalind Franklin and colleagues published papers in the journal Nature on the structure of DNA. Furthermore, on
History of molecular biology modeling efforts of Watson and Crick. In their modeling, Watson and Crick restricted themselves to what they saw as chemically and biologically reasonable. Still, the breadth of possibilities was very wide. A breakthrough occurred in 1952, when Erwin Chargaff visited Cambridge and inspired Crick with a description of experiments Chargaff had published in 1947. Chargaff had observed that the proportions of the four nucleotides vary between one DNA sample and the next, but that for particular pairs of nucleotides — adenine and thymine, guanine and cytosine — the two nucleotides are always present in equal proportions. Using X-ray diffraction, as