Final answer:
The scientists directly involved in discovering the structure of DNA were James Watson, Francis Crick, and to an uncredited but significant extent, Rosalind Franklin, with their model relying on Franklin's X-ray diffraction images.
Step-by-step explanation:
The three scientists who were closely involved in discovering DNA as genetic material include Oswald Avery and his colleagues Colin MacLeod and Maclyn McCarty, who demonstrated that DNA carried genetic information following the earlier findings of Frederick Griffith, along with Alfred Hershey and Martha Chase who confirmed that DNA was the genetic material with their bacteriophage experiments, and Erwin Chargaff who discovered key principles about the base composition of DNA.
However, when considering the structure of DNA, we think of James Watson, Francis Crick, and Rosalind Franklin. Watson and Crick were responsible for piecing together the double helix model of DNA, and their work was heavily based on the X-ray diffraction images of DNA produced by Franklin. Although it was Watson, Crick, and Maurice Wilkins who were awarded the Nobel Prize in Medicine in 1962, Franklin's crucial contributions to the discovery of the double helix structure of DNA went without Nobel recognition.