The popular terms genetic engineering and genetic modification refer to a biotechnology that manipulates genetic material. This includes altering the DNA of an organism many copies of the protein the foreign DNA specifies. In the 1980s, researchers began to apply recombinant DNA technology to multicellular organisms, producing transgenic plants and animals. Researchers add foreign DNA at the one-cell stage (a gamete or fertilized ovum). The transgenic organism that develops from the original altered cell carries the genetic change in every cell. Yet another biotechnology, called gene targeting, adds precision to transgenic technology. Gene targeting \u201cknocks out\u201d or \u201cknocks in\u201d the gene of interest at a particular chromosomal locus, where it trades places with an existing gene.