As has repeatedly been stated, the underlying hypothesis, which in a number of cases has been supported by direct experimental evidence, is that each gene controls the production, function, and specificity of a particular enzyme.

Beadle and Tatum's key experiments involved exposing the bread mold Neurospora crassa to x-rays causing mutations. Tatum was born in Boulder Colorado. He attended college at the University of Chicago and received his PhD in biochemistry from the University of Wisconsin–Madison in 1934.

In a series of experiments they showed that these mutations caused changes in specific enzymes involved in metabolic pathways. The other half of that year's award went to Joshua Lederberg. An active area of research in his laboratory was to understand the basis of Tryptophan biosynthesis in Escherichia coli.