Genetically engineered foods have had foreign genes inserted into their genetic codes artificially. Genetic engineering can be done with plants, animals, or micro-organisms. Historically, farmers bred plants and animals for desired traits for thousands of years. They would produce dogs ranging from poodles to Great Danes, for example and roses from sweet-smelling miniatures to today's long-lasting, but odor-free reds. Selective breeding over time created these wide variations, but it is dependent on nature producing the desired gene and humans choosing to mate animals or plants with that gene to make the related characteristics more common or more pronounced. Genetic engineering allows scientists to speed this process up by moving desired genes from one plant into another -- or even from an animal to a plant or vice versa.