A gene, one enzyme. A gene, a polypeptide
In the 1940s, it was demonstrated that the enzyme defect was recessive hereditary and that the genes, of Dane Johanson in 1910 baptized in a gene (non gene, as it says englifisert), may have the function to control an enzyme.
In the 1950s it was discovered that the disease was "molecular" because an amended charge of the protein in the blood pigment to give harmful effect and followed the simple inheritance: dominant for an innocent trait, but recessive (in double dose) for a deadly form of anemia.
From this came the discovery that a functional gene did was code for a protein chain: one gene - one polypeptide. Damage in the gene for an enzyme was its proteindel and gave a double dose of an enzyme defect.