Genetic engineering is the human altering of the genetic material of living cells to make them capable of producing new substances or performing new functions. The technique became possible during the 1950s when Francis Crick (1916-) and James Watson (1928-) discovered the structure of DNA molecules. Crick, Watson and later researchers learned how these molecules store and transmit genetic information.
DNA (deoxyribonucleic acid) is found in the nucleus of all living cells. It is structured as a double helix, with two twisted strands parallel to each other with rungs like a ladder between the strands. Each strand consists of four chemical bases: guanine (G), adenine (A), thymine (T) and cytosine (C). These bases are repeated in particular arrays of sequences throughout the DNA molecule. The patterns they create provide the instructions on how cells will develop and what their tasks will be. DNA is packed into structures called chromosomes within the cell.
Genetic engineering allows scientists to identify specific genes, remove them, and clone (duplicate) them and use them in another part of the same organism, or in an entirely different one. For instance, cells of bacteria colonies can be changed by genetic engineering to produce proteins, hormones or other substances that may be useful in treating illnesses in humans or other animals.
This process is called gene splicing or recombinant (as in recombining) DNA technique. Genetic engineers can also increase the amount of certain antibodies for treatment by using hybridomas (altered rapidly growing cancer cells and cells that make antibodies) to form monoclonal anti-bodies. They can also use the polymerase chain reaction technique to make perfect copies of DNA fragments from very small samples so that the origin of the substance (hair, blood) can be identified. This procedure is used in DNA fingerprinting in criminal cases.
Cloning and Engineering
Although the structure of DNA was discovered in the 1950s, it was not until the early 1970s that scientists figured out how to clone and engineer genes. The first experiments were done with simple organisms such as bacteria, viruses and plasmids (rings of free DNA in bacteria). Hamilton 0. Smith, Daniel Nathans and Werner Arber were the first researchers to realize that the bacteria made enzymes, called restriction enzymes, that would "cut" DNA chains in specific places. The scientists could then use these enzymes to cut the DNA into segments, cut out a segment that gave disease-causing instructions, and replace it with a segment that gave correct instructions for healthy functioning.
One could also use this technique to alter a bacterium to perform a certain function (such as making insulin for sugar metabolism) and then reproduce itself many times to provide this hormones for treating diseases such as diabetes. There are limits to this ability, however. Scientists must start with a complete organism, and cannot change everything in it. They can only make a limited number of changes, so the organism can remain essentially the same. Our knowledge of the total genetic code for humans, which contains millions of patterns is limited, so we cannot transfer complicated traits like intelligence, which are a mixture of genetic and environmental influences.
One of the most exciting potential applications of genetic engineering involves the treatment of genetic disorders. Medical scientists now know of about 3,000 disorders that arise because of errors in an individual's DNA. Conditions such as sickle-cell anemia, Tay-Sachs disease, Duchenne muscular dystrophy, Huntington's chorea, cystic fibrosis, and Lesch-Nyhan syndrome are the result of the loss, mistaken insertion, or change of a single nitrogen base in a DNA molecule.
Genetic engineering makes it possible for scientists to provide individuals who lack a certain gene with correct copies of that gene. For instance, in 1990 a girl with a disease caused by a defect in a single gene was treated in the following fashion. Some of her blood was taken, and the missing gene was copied and inserted into her own white blood cells, then the blood was returned to her body. If—and when—that correct gene begins to function, the genetic disorder may be cured. This type of procedure is known as human gene therapy (HGT).
Genetic engineering also promises a revolution in agriculture. It is now possible to produce plants that will survive freezing temperatures, take longer to ripen, convert atmospheric nitrogen to a form they can use, manufacture their own resistance to pests, and so on. By 1988 scientists had tested more than two dozen kinds of plants engineered to have special properties such as these. Domestic animals have been genetically "engineered" in an inexact way through breeding programs to create more meaty animals, etc., but with genetic engineering, these desirable traits could be guaranteed for each new generation of animal.
The potential commercial value of genetically-engineered products was not lost on entrepreneurs (business starters) in the 1970s. A few individuals believed that recombinant DNA would transform American technology as computers had in the 1950s. In many cases, the founders of the first genetic engineering firms were scientists themselves. They were profiting from research that was originally paid for in large part with government funds.
As a result, some have questioned whether individual scientists have the right to make a personal profit from these techniques. As of the early 1990s, working relationships had, in many cases, been formalized among universities, individual researchers, and the corporations they established. But not every-one is satisfied that the ethical issues involved in such arrangements are settled.
Many critics also worry about where genetic engineering might lead. If we can cure genetic disorders, can we also design individuals who are taller, more intelligent, or better looking? Is that a good application of the technology? Will the altered agricultural products be safe for humans, or will they change us in some unknown way? Will the altered bacteria used to create synthetic versions of substances such as insulin create new bacteria that are harmful to humans? Will humans know when to say "enough" to the changes that can be made? These are some of the ethical questions that surround genetic engineering.
Many other applications of genetic engineering have already been developed or are likely to be realized in the future. In every case, however, the glowing promises of each new technique are balanced by the new social, economic, and ethical questions that are being raised.