Answer:
"One gene, one enzyme" hypothesis says that one gene encodes for one protein which performs a specific function in the living organisms. This study, published in 1941, was one of the most influential studies of the age and for that, Beadle and Tatus also received Nobel Prize.
However, in recent years, it has been well studied that many enzymes are encoded by more than one gene (or cluster of genes). There are some enzymes that are produced by a single gene; nevertheless, it has been concluded that the hypothesis is not completely true. But it is also important to say that this study set the baseline for the study of many biochemical processes in living organisms.