Between 1934 and 1945, George Beadle developed a hypothesis that each gene within the chromosomes of organisms each produced one enzyme. Enzymes are types of proteins that can catalyze reactions inside cells, and the figure shows that each enzyme controls a stage in a series of biochemical reactions. The top box in this figure represents a normal process of enzyme production and biochemical reactions, and the bottom box shows how Beadle's experiments affected the normal biochemical process.

The male body, followed by male reproductive organs from which the sperm originates, is depicted from top to bottom at the left. Under the male reproductive organs is a diagram of a single sperm. To the right of the sperm diagram, the physiological and morphological changes a sperm undergoes to fertilize an egg are depicted from left to right. Each change is associated with a light pink rectangle background. Each light pink rectangle corresponds to the location of the sperm within the female reproductive organs, which is depicted above it.