Many new biotechnologies do not involve modifications of traits passed on to the next generation. A good example is monoclonal antibodies (highly specific preparations of antibodies that bind to a single site on a protein), which have many diagnostic applications, including home pregnancy testing kits. Many biotechnology companies are engaged in these sophisticated, but noncontroversial, technologies.

By contrast, mammalian cloning is a new biotechnology that does not involve gene modification, but is nevertheless highly controversial. Cloning reproduces adult mammals by transplanting a nucleus from adult cells into an egg from which the nucleus has been removed and allowing the egg to develop in a surrogate manner.

The resulting individuals are as similar to the adults from which the nuclei were taken as identical twins are to one another. Although this procedure has profound implications for human reproduction, it does not modify specific traits of an individual, but rather transfers a whole nucleus containing a complete set of genetic information.

The new technology that can affect future generations is genetic engineering, a technology based on the artificial manipulation and transfer of genetic material. This technology can move genes and the traits they dictate across natural boundaries-from one type of plant to another, from one type of animal to another, and even from a plant to an animal or an animal to a plant. Cells modified by these techniques pass the new genes and traits on to their offspring. Genetic engineering can apply to any kind of living organism from microorganisms to humans.

Genetic engineering can be applied to humans to replace or supplement defective genes. Where engineering is intended to cure disease, it is called gene therapy. Potential applications that are not related to disease, such as the modification of traits like height, are sometimes called genetic enhancement. Currently, most genetic engineering of humans is done on nonreproductive or somatic cells, like those from bone marrow. The effects of this somatic cell gene therapy are confined to the treated individual. By contrast, germ line gene therapy would modify reproductive cells, so that the modification could be passed on to future generations.