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,
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.