Although human beings have been modifying the genetics of plants and animals for thousands of years through selective breeding, genetic modification, as now applied, refers to the introduction of specific foreign genes into an organism's genome through the techniques of molecular biology. Genetic engineering of organisms began in earnest in the 1970s with the ability of scientists to clone genes and insert them in bacteria. Such "transgenic" organisms could be made to produce the gene products of the inserted gene, allowing scientists to produce drugs such as human insulin and other biochemical products with ease. Soon after, scientists were inserting genes into mouse embryos to produce transgenic animals for research. Other molecular biology techniques allowed scientists to "knockout" genes of interest to see what effect their removal had upon specific disease processes. In our laboratory, we use cloning and genetic engineering to produce both transgenic and knockout mouse models to study inflammatory bowel diseases. Obviously, not all genetic modification of organisms is bad, since these GMOs have led to breakthroughs in medical research.