Commercial recombinant DNA technology was first used to produce human insulin in bacteria. In 1982, genetically engineered insulin was approved by the FDA for use by diabetics. Insulin is normally produced by the pancreas, and for more than fifty years the pancreas of slaughtered animals such as swine or sheep was used as an insulin source. To provide a reliable source of human insulin, researchers harvested the insulin gene from cellular DNA; they made a copy of DNA carrying this insulin gene and spliced it into a bacterium. When the bacterium was cultured, the microbe split from one cell into two cells, and both cells got a copy of the insulin gene. Those two microbes grew, then divided into four, those four into eight, the eight into sixteen, and so forth. With each cell division, the two new cells each had a copy of the gene for human insulin. Because the cells had a copy of the genetic “recipe card” for insulin, they could make the insulin protein. In fact, in this case, using genetic engineering to produce insulin was both cheaper and safer for patients, as some patients were allergic to insulin from other animals.