"one gene-one enzyme” hypothesis. This hypothesis has undergone some important updates since Beadle and Tatum

1. Some genes encode proteins that are not enzymes. Enzymes are just one category of protein. There are many non-enzyme proteins in cells, and these proteins are also encoded by genes. 2. Some genes encode a subunit of a protein, not a whole protein. In general, a gene encodes one polypeptide, meaning one chain of amino acids. Some proteins consist of several polypeptides from different genes 3. Some genes don't encode polypeptides. Some genes actually encode functional RNA molecules rather than polypeptides!