Insulin, synthesized by the beta cells of the islets of Langerhans, consists of 2 dissimilar polypeptide chains, A and B, which are linked by 2 disulfide bonds. The insulin gene contains 3 exons and 2 introns; exon 2 encodes the signal peptide, the B chain, and part of the C peptide, while exon 3 encodes the remainder of the C peptide and the A chain. Localization of the human insulin gene to the distal end of the short arm of chromosome 11. Harper et al. (1981) and Harper and Saunders (1981) assigned the insulin gene to 11p15.5 by in situ hybridization.