Although it was originally thought that protein could be the genetic material carrying hereditary information in cells, through the 20th century it became increasingly clearer that DNA must be the genetic material.
It was thought that knowing the structure of the molecule would reveal how that information is stored and used in the cell. A number of researchers in the 1940s and early 1950s worked toward discovering the structure of DNA.
discovered that DNA has approximately equal amounts of A and T bases, as well as approximately equal amounts of C and G bases. Two years later, X-ray crystallography on DNA performed by
led to photograph 51, an image taken by doctoral student
that revealed information about the shape and dimensions of the DNA molecule. Later, the photograph was shown to
who used the information gleaned from it to propose, along with
, the familiar double helical model of DNA.