The genetically modified organism primarily used to make insulin is Escherichia coli (E. coli), a type of bacteria. Scientists have engineered specific strains of E. coli to carry the human gene responsible for producing insulin, which is critical for regulating blood glucose levels in people with diabetes. By inserting the insulin gene into E. coli, these bacteria can be cultured to produce insulin in large quantities. This biotechnological approach has revolutionized diabetes treatment, enabling the mass production of human insulin with fewer allergens and more consistent results compared to previous animal-derived insulin sources.