To analyze regulatory mutants of the lac operon, Jacob developed a system by which a second copy of the lac genes (lacI with its promoter, and lacZYA with promoter and operator) could be introduced into a single cell.
Para analizar os mutantes reguladores do operón lac, Jacob desenvolveu un sistema polo cal podía introducirse unha segunda copia dos xenes lac (lacI co seu promotor, e lacZYA co seu promotor e operador) nunha soa célula.