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Genetically Modified Foods and Organisms

crops transgenic dna plant

While the term genetically modified organisms has arisen within the past decade, humans have for centuries been using microorganisms to make products like beer and cheese, and plants and animals have been carefully bred to improve the quality and quantity of the food supply. The elucidation of the structure of DNA and the development of the discipline of molecular biology has made possible the accurate insertion or removal specific genes into or out of the DNA of particular organisms. This enables the design organisms with specific desirable characteristics and the ability to understand which genes control the growth, reproduction, and aging and disease susceptibility of plants and animals.

Aside from foods, genetically modified organisms are making their way into other commercial venues. For example, the forestry industry is actively utilizing molecular biology to generate trees capable of faster and straighter growth.

The use of genetically modified organisms in agriculture has expanded at a rapid rate in key agricultural exporting countries in the past decade. Countries where transgenic crops are in advanced stages of field-testing or commercialization include the United States, Argentina, Canada, and Australia. The global area devoted to transgenic crops has increased from 1.7 hectares in 1996, to 27.8 hectares in 1998. In North America, the use of genetically modified cotton, soybean and canola now represents some 50 percent of the total acreage.

Genetically modified organisms have generated considerable debate.

Critics on one side of the debate contend that number of countries without a strong scientific infrastructure fear genetically modified foods. Others countries with advanced scientific and medical research infrastructure, (e.g., France and other European Union countries) have passed laws regulating genetically modified organisms for economic and political reasons (e.g. as a form of protectionism for their less progressive agricultural systems.) In 2001 and 2002, European countries, including France and Germany, pushed for tough European Union rules regulating the sale of genetically modified foods. The US State Department branded the news rules as "unnecessary" and without scientific merit. The US has already warned that a trade war over "biotechnology foods" might develop if the European Union fails to lift blocks to imports.

In 2002, reports surfaced that French scaremongering concerning genetically modified foods caused several African countries fighting starvation to reject genetically modified food supplements that would have reduced starvation and death rates.

On the other side of the debate, critics argue that the impact of these totally new organisms on the environment and on human health cannot presently be completely predicted. Within recent years several studies have purported to demonstrate harmful effects to monarch butterflies by their ingestion of pollen from Bt corn (corn modified by a bacterium called Bacillus thuringiensis(Bt)), and to rats by their ingestion of modified potatoes. The validity of these studies remains controversial. As well, the increased yields of genetically modified organisms may contribute to a decrease in crop biological diversity—genetic differences between species. Homogeneity may make crops more susceptible to disease. Thus, the present uncertainty about the cumulative effects in ecosystems or the food chain is making consumers wary.

Considerable controversy has arisen concerning the genetic modification of plants such that their seeds are not capable of growth upon planting. The commercial control and potential monopolization of food production has been decried by some. Some critics also point out that prudence on the part of France and other countries reflect warranted scientific prudence that also continues to respect closer cultural ties to food and agricultural production.

In January, 2000, The Cartagena Protocol on Biosafety was adopted in Montreal, Canada. The protocol, negotiated under the United Nations Convention on Biological Diversity, is one of the first legally binding international agreements to govern the trade or sale of genetically modified organisms of agricultural importance.

Such social, political and legal debates surrounding genetically modified organisms will likely not be resolved soon.

It is scientifically demonstrated that genetically modified crops are resistant to or tolerant to disease or insect attack. For example, a gene encoding an insecticidal protein from the bacterium Bacillus thuringiensis (Bt) has made cotton, corn and other crops resistant to attack by caterpillars. Data from several years of use of genetically modified crops in the Unites States has shown that the requirement for pesticides is reduced. Genetically modified crops may also permit higher yields. This may offer real hope to the estimated billion people who are chronically under-nourished and hungry, and to the many more as the global population doubles in the next 50 years. Additionally, crops that have improved nutritional value or with therapeutic value are being designed. Such nutraceuticals are driving the development of an industry whose annual sales are expected to grow to billions in the United States alone.

The direct genetic modification of foods is a modern extension of agricultural practices that have long selected genetically controlled traits of agriculturally relevant plant and animal species, so as to instills in these species beneficial genetic traits (often found in other organisms). Techniques to analyze genetic material developed within the last twenty years allow a quicker and accurate identification and propagation of superior traits, speeding the overall process of genetic improvement.

Transgenic crops (also called genetically modified crops) contain genetic material from some source other than themselves (all crops have been somewhat genetically modified from their original wild state by domestication, selection and controlled breeding over long periods of time). The inserted gene sequence, called a transgene, may come from another related species, or from a completely different species, such as a bacterial cell.

A significant advance in agricultural genetics has been the harnessing of transgenic crops to express biopesticides (also known as biological pesticides). At the end of 1998, there were approximately 175 registered biopesticide active ingredients and 700 products. The three main classes of biopesticides are microbial pesticides (microorganism as the active ingredient), biochemical pesticides (natural and non-toxic compounds as the pest control agent) and plant pesticides. Herbicide resistance is a popular transgenic trait. Plants have been engineered to be resistant to herbicides like glyphosate or glufosinate, which are broad spectrum in their activity, killing nearly all kinds of plants except those possessing the resistance transgene. Another popular biopesticide target is insects, such as European corn borer and the cotton bollworm, which can be killed by a protein produced by Bacillus thuringiensis(Bt).

Once a useful gene has been identified, isolated and copies made, it must be modified so it can be effectively inserted into the DNA of the target plant or animal. An efficient on-off switch for the expression of the gene is added to one end of the gene. A commonly used promoter sequence is CaMV35S from the cauliflower mosaic virus. At the other end of the gene a sequence is added which signals an end to expression. The gene can also be modified slightly to increase its expression. In the same stretch of DNA as the above construct lies a marker gene, complete with its own promoter and termination sequences. The marker gene codes for resistance to a selected antibiotic or herbicide. Development of resistance following transformation means that the inserted DNA has been expressed.

The new genetic material is inserted into the plant or animal genetic material in a process called transformation. The two main methods of transformation are the gene gun method and the Agrobacterium method. In the first, millions of DNA-coated particles are shot from a specialized gun inside the plant or animal cell. Some of the DNA will recombine with the cellular DNA. The second method takes advantage of the ability of a soil bacterium called Agrobacterium tumefaciens to inject, through a wound in plant cells, a specialized portion of its DNA. Following transformation, plant tissues are transferred to a growth source containing the selective antibiotic or herbicide. Cells which grow are those in which the foreign DNA has been expressed. Before the transgenic cell is ready for commercial use it must be rigorously verified and demonstrated to legislative authorities that the transgene has been stably incorporated, and does not pose harm to other plant functions, final product or the natural environment where it will reside. Often the transgenic crop will be crossed with existing parents to produce an improved variety. The improved variety is then used for several cycles of crosses to the parent to recover as much of the improved parent's genetic material as possible, with the addition of the transgene.

Development of transgene technology has been slowed by the limited knowledge of the complexities of gene expression, with the myriad of other factors, some responsive to environmental change, which control the gene's expression. Despite this limitation, the early successes of the technology have met with great commercial acceptance. As of 2000, the most popular transgenic crop and trait worldwide in terms of acreage planted is soybean (more than 55 million acres) and herbicide (more than 70 million acres). Total worldwide acreage of transgenic crops in 2000 was approximately 166 million acres. In that year, almost half of the United States' soybean crop and about 28 % of its corn crop were transgenic varieties. One attraction has been the savings in pesticide use. In the case of cotton, the use of the Bt crops has dramatically reduced the amount of chemical pesticides used.

Resources

Books

Ruse, Michael and David Castle, eds. Genetically Modified Foods: Debating Biotechnology Contemporary Issues Series, Amherst, NY: Prometheus Books, 2002.

Nelson, Gerald C., ed. Genetically Modified Organisms in Agriculture: Economics and Politics San Diego, CA: Academic Press, 2001.

Other

American Society for Microbiology. "Statement of the American Society for Microbiology on Genetically Modified Or ganisms" [cited February 27, 2003]. <http://www.asmusa.org/pasrc/genmodorg.htm>.

Untied States Department of Energy Office of Science. Human Genome Project Information. "Genetically Modified Foods and Organisms" [cited February 27, 2003]. <http://www.ornl.gov/hgmis/elsi/gmfood.html>.


Brian Hoyle
K. Lee Lerner

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about 6 years ago

this was very helpful thanks i got an A on my project.. thanks you guys....