Gene splicing is a technique used in genetic engineering where the DNA of a living thing is edited, in some cases replacing existing genes with genes taken from another plant or animal. Enzymes are used to cut the DNA strand and remove a piece, which can then be replaced with new information. This can transfer characteristics from one species to another or give an organism entirely new characteristics.
One famous example of gene splicing was the implantation of an antifreeze gene into tomatoes, creating a frost-resistant fruit. Since the antifreeze gene originally came from a fish adapted to thrive in cold waters, opponents of genetic modification began calling the result a "fish tomato," despite the fact that no fish characteristics were actually transferred into the plant. Another example involves the transference of bioluminescent genes into various organisms to aid in studying their life processes in the laboratory.
In some cases, entirely new genes are created to be spliced into the organism's DNA. The biotech firm LS9 created an entirely synthetic batch of genes to plant into a sugar-eating bacterium, causing the microorganism to excrete a compound functionally identical to diesel fuel. Other bacteria have been altered to produce lifesaving medicines, and another project re-engineered the bacterium responsible for tooth decay to halt its production of lactic acid, eliminating its ability to damage tooth enamel.