A. Griffith- discovered DNA transfer in bacteria
B. Chargaff- discovered base-pairing rules (A-T) (G-C)
C. Franklin and Wilkins- took x-ray crystallography of DNA
D. Watson and Crick- used the previous work of Chargaff, Franklin and Wilkins to discover double helix structure
Hope this helps, and let me know if you have any more questions! :)
