A unit of heredity must carry the code to build a metabolic or cellular function specified by a protein. “A gene,” Beadle wrote in 1945, “can be visualized as directing the final configuration of a protein molecule.” This was the “action of the gene” that a generation of biologists had been trying to comprehend: a gene “acts” by encoding information to build a protein, and the protein actualizes the form or function of the organism.
