Introduction

By selecting organisms with the most desirable qualities, mankind began the process of genetic engineering thousands of years ago with the domestication of animals and the advent of farming. Until the development of recombinant DNA technology, this process has been relatively slow. Now we possess the ability to custom-tailor life, with the only limit being that of our imaginations.

Current Usage

Genetic engineering is widely used to produce plants and animals with better nutritional values. More recently, plants and animals have been altered to contain completely new traits. Mouse genes are often recombined to produce human proteins and tumors and basically imitate human illnesses for study and medicinal trials. Cows, sheep, and goats are being altered to produce blood-clotting factors in their milk for human use.

By far, the largest use of recombinant DNA technology has been in the agricultural industry. Chemical industries like Du Pont, Cargill, Novartis, and Monsanto have been able to make very successful improvements in plants. Monsanto, in particular, has been able to produce a plant that is lethal to its most common pests and resistant to certain herbicides.

Many insects have a unique ion pump in the cells that line the columnar epithelial cells of the salivary glands and midgut. A bacterium, Bacillus thuringiensis, produces a protein that inhibits the ion channels of these epithelial cells. This adaptation benefits the bacterium by insuring that a specific insect feeding on the colony will be unable to eat within hours due to the protein and its paralyzation of the digestive system. Farmers have previously utilized the production of the delta-endotoxin protein, CrylA(b), by spraying their crops with B. thuringiensis to protect against the caterpillar stages of many insects. This protein has been isolated on a gene, called Bt, in the plasmids of the bacterium. The gene has been genetically "sewn" into the genome of certain crops, giving them resistance to certain pests without ever needing to be sprayed.

Monsanto’s creation has another engineered property that allows the crop to live uninhibited, as all unwanted weeds shrivel under the application of a herbicide. Monsanto’s herbicide glyphosate, known commonly as Roundup (C3H8NO5P), kills bacteria and plants by inhibiting the EPSP Synthetase of the aromatic amino acid pathway. Bacteria with an altered EPSP Synthetase are unaffected by glyphosate. The genetic engineering of this altered EPSP Synthetase into crops enables them to be sprayed by glyphosate, which allows no chance for the survival of unwanted plants in farmlands. Corn and soybean are commonly used with these dual defenses. Tomatoes, squash, canola, sugar, rice, beets, and potatoes have been engineered for certain properties as well.

Process of Genetic Engineering

Currently, genetic engineering is enabled by some of nature’s own genetic engineers. The bacterium Agrobacterium tumefaciens recombines the DNA of plants to cause the plant cells to produce specific chemicals. This adaptation benefits the bacterium by turning the plant’s cells into opine-producing tumors. The opine is then consumed by the bacterium. Modern science has simply altered the plasmid’s directions for making the opine produce chemicals more beneficial to mankind. In animals, cancer-causing retroviruses are used in the same way to alter the genome of an organism.

In the case of Bt‘s transfer, first the gene must be isolated and cut from the plasmid of Bacillus thuringiensis using a restriction enzyme. This enzyme produces a fragment containing a specific, single-stranded nucleotide sequence at the 5’ end of the chain (e.g., AGTA on one strand and TCAT on the other). This fragment is then attached to the gene encoding resistance to a certain drug, such as tetracycline. The combined fragment is then added to the plasmids, called Ti, of A. tumefaciens. These plasmids were cut using the same restriction enzyme. The complementary nucleotides attract one another by base pairing, and bind covalently with the addition of DNA ligase to seal the single-stranded ends together. To weed out those bacteria that did not properly incorporate the DNA fragment into their plasmids, tetracycline is added. Those bacteria that survive have attained the resistance to the tetracycline and the desired Bt gene as well. The genetically engineered A. tumefaciens can now be placed onto a culture of plant cells. These cultured cells can be grown into adult plants that will produce the Bt protein CrylA(b) and have the genetically engineered ability to kill certain insects if eaten.

In animals, the process is a bit more difficult. A retrovirus is constructed to alter the animal cells. Usually, cells are taken from the blastula of a developing embryo and transformed, via the virus’s infection. These cells are then reinserted into another blastula. It is then hoped that the transformed cells end up becoming the reproductive organs of the chimeric organism, so that they can breed to produce offspring possessing only the transformed DNA. Recently, this process has been simplified with the advent of cloning. Cells of a full-grown individual can be infected with a retrovirus and cloned to produce an "identical" organism with the desired genetic transformation.

Pros and Cons of Genetic Engineering

Scientifically, the use of genetic engineering could lead to many problems. The genetic diversity of crops will continue to decline. The loss of diversity means that farmlands will be at a greater risk to infections, inclement weather, and new pests. If one plant is not resistant to a new condition or threat, none of the others will be, either. There are also the secondary ecological effects of starving off all of these "pests": The insects being killed may help to pollinate other species of plants or provide food for birds.

Environmentalists have brought to light the problems with current commercial genetic engineering. Milkweed dusted with engineered corn pollen kills monarch butterfly larvae. The specificity of the Bt protein is now in doubt. Other problems include the spraying of Roundup over large areas. Additionally, it has been claimed that Roundup causes illness in farm and landscape workers. Traces of it have been found up to a year after spraying. Also, natural resistance to Roundup has occurred in Australian ryegrass.

An even greater concern is the possibility that the retroviruses and bacteria used to produced the engineered plants and animals could wreak havoc on the environment. The scientifically designed vectors are much less specific then their natural counterparts. The creation of new organisms that can easily carry genes from one species to another drastically increases the chances of diseases infecting new species that were previously out of their reach. The newly infected species would have no defense against such a disease.

One bright side of genetically engineered foodstuffs is the introduction of the genes for making beta-carotene, the precursor of Vitamin A, into rice, a project supported by the Rockefeller Foundation. This type of transgenic rice, termed "golden rice" because of thits yellowish tint from the beta-carotene content, has the potential to provide sufficient Vitamin A precursors in a typical high rice content Asian diet to meet all the daily requirements for this vitamin. To the close to two hundred million children in developing countries who suffer from Vitamin A deficiencies, resulting in more then two million deaths annually, these new rice strains can literally be a life saver.

The United States seems reluctant to regulate the field, but Europe and Asia have taken a more cautious approach. Japan has suspended the use of Bt crops until further studies have been completed. France and Britain have placed a moratorium on the production of certain transgenic crops. Other European companies in Germany and Switzerland have stopped the purchase of American genetically modified crops due to public pressure. Public pressure in the United States does not appear to be enough to hinder the production of even more genetically altered crops and animals. Whether this path unlocks the doors to society’s dreams or nightmares remains to be seen.

Genetic Engineering Web Links

Intekom - U.S. chemical giant Monsanto wields control.

Insect Control - Insects controlled by Bacillus thuringiensis.

rDNA Tech - General method of rDNA technology using plasmids.

Scientific American - Poison plants?

Spectrum - Glyphosate chemical fact sheet.

Plant Biotechnology - A recent balanced summary from the Rockefeller Foundation.

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