Genetically Modified Foods
Genetically Modified Foods
Genetic modification employs recombinant deoxyribonucleic acid (rDNA) technology to alter the genes of microorganisms , plants, and animals. Genetic modification is also called biotechnology, gene splicing, recombinant DNA technology, or genetic engineering. Contemporary genetic modification was developed in the 1970s and essentially transfers genetic material from one organism to another. The modification of organisms has existed for centuries in the form of plant-breeding techniques (such as cross-fertilization) used to produce desired traits. With genetic modification, however, isolated genes are inserted into plants for a desired trait with a much quicker result than occurs when cross-breeding plants, which can take years. These isolated genes do not have to come from similar species in order to be functional; theoretically, genes can be transferred among all microorganisms, plants, and animals.
Examples of Genetically Modified Foods
Crops may be modified to increase resistance to pests and disease, increase adaptability to environmental conditions, improve flavor or nutritional profile, delay ripening, or increase shelf life. Many common crops are genetically modified, such as corn, canola, flax, potatoes, tomatoes, squash, and soybeans. Corn and potatoes may be modified with a gene to produce an endotoxin that protects them against the corn-borer pest and the potato beetle, respectively. A soybean can be genetically modified with a gene from a bacterium to make it herbicide resistant. By inserting two genes from daffodil and one gene from a bacterium, rice can be enriched with beta-carotene.
In the early 1990s, genetically modified tomatoes (Flavr Savr by Calgene, Inc.) were deemed safe by the U.S., Canadian, and British governments and introduced into the market. These tomatoes were bred to stay firm after harvest so they could remain on the vine longer and ripen to full flavor. However, the tomatoes were so delicate that they were difficult to transport without damage, and the product was pulled from the market in 1997.
Recombinant bovine growth hormone (rBGH), also known as recombinant bovine somatotropin (rBST), is another example of a product that has not been very successful. Recombinant BGH (Posilac by Monsanto Company) is a genetically engineered version of a growth hormone that increases milk output in dairy cows by as much as 10 to 30 percent. In 1999 the United Nations Food Safety Agency unanimously declared the use of rBGH unsafe after confirming reports of excess levels of the naturally occurring insulin-like growth factor one (IGF-1), including its highly potent variants, in rBGH milk and concluding that these posed major risks of cancer . Health Canada also banned the use of rBGH in milk production in 1999, but the hormone is still permitted in the U.S. milk supply.
Safety of Genetically Modified Foods
Biotechnology has moved at such a rapid pace that the safety of genetically modified foods has become a concern. At this time, there are no long-term, large-scale tests to prove their safety—or lack thereof. Unforeseen consequences may arise from widespread genetic modification of the food supply, including:
- •Allergic reaction . If a gene producing a protein that causes an allergic reaction is engineered into corn, for example, an individual who is allergic to that protein may experience an allergic reaction to the corn. Despite the fact that food-regulating agencies require companies to report whether altered food contains any suspect proteins, unknown allergens could potentially slip through the system.
- Increased toxicity. Genetic modification may enhance natural plant toxins in unexpected ways. When a gene is switched on, besides having the desired effect, it may also stimulate the production of natural toxins.
- Resistance to antibiotics . As part of the genetic modification of organisms, marker genes are used to determine if the desired gene has been successfully embedded. Marker genes typically provide resistance to antibiotics. Even though marker genes are genetically scrambled before use to reduce the potential for this danger, their use could contribute to the growing problem of antibiotic resistance.
- Herbicide-resistant weeds. Once modified crops are planted, genes may travel via airborne, waterborne, or animal-borne seeds and pollen to weedy relatives, creating "superweeds" that are able to resist herbicides.
- Harm to other organisms. Nontargeted species may inadvertently be harmed by a genetically modified plant producing endotoxins intended for a specific pest. For example, nearly all insect-resistant plants contain a gene from the bacterium Baciullus thuringiensis (Bt), which results in the production of a natural endotoxin that is toxic to all insects. The Bt endotoxin is widely used by organic and conventional farmers because it is a relatively harmless, natural pesticide. However, genetically modified plants such as Bt corn, cotton, potatoes, rice, and tomatoes constantly produce the Bt endotoxin, and thus speed up the spread of Bt resistance among pests that feed on these
- plants. They may also reduce insect diversity and population numbers among harmless and beneficial insects.
- Pesticide-resistant insects and the demise of safe pesticides. Most of the common genetically modified crops contain a gene that produces a protein which is toxic to a specific pest. However, exposing pests to toxins may stimulate resistance by the pests and render the pesticides useless.
Typically, when a new crop is created, whether by traditional methods or genetic modification, breeders conduct field testing for several seasons to make sure only desirable changes occur. Appearance, growth characteristics, and taste of the food are checked, and analytical tests to determine changes in nutrients and safety are performed. According to the U.S. Department of Agriculture, there is no evidence that any genetically modified foods now on the market pose any human health concerns or are in any way less safe than crops produced through traditional breeding. In 2002, however, the European Union updated and strengthened existing regulations and labeling laws for genetically modified foods in the European markets.
The Food and Agriculture Organization (FAO) of the United Nations recognizes that genetic engineering has the potential to help increase productivity in agriculture, forestry, and fisheries. However, the FAO urges caution to reduce the risks associated with transferring toxins from one organism to another, of creating new toxins, or of transferring allergenic compounds from one organism to another. The FAO acknowledges potential risks to the environment, including outcrossing (crossing unrelated organisms), which could lead to the evolution of more aggressive weeds, pests with increased resistance to diseases, or environmental stresses that upset the ecosystem balance.
Labeling of Genetically Modified Foods
According to the Institute of Food Technologists, genetically modified foods should not be labeled because "labels are likely to mislead consumers by implying a warning. . . . Moreover, labeling rDNA-engineered foods would not be economically prudent." In the European Union, concern about the safety of genetically modified organisms, fanned by years of political activism, has resulted in regulations that keep many genetically modified foods out of the European market. These regulations include requirements for tracing the genetic origin of each food ingredient, and for labeling the resulting products accordingly. Fueled by consumer protest and demand, lawmakers in China and Canada have recently begun discussing stricter labeling laws as well.
The Acceptance of Genetically Modified Foods
In the United States, only limited objections have been raised to genetically modified foods, which can be more nutritious, disease-resistant, flavorful, or cheaper than natural foods. In Europe, by contrast, consumers and governments have focused on the potential dangers of genetic modification, which include unforeseen resistance to antibiotics and herbicides, the spread of dangerous allergens, and damage to livestock, public health, and the environment. Health disasters such as the mad cow outbreak have left many European consumers with a distrust of corporations and regulatory bodies and a determination to understand where their food comes from. While some genetically modified crops are allowed in Europe, the European Union has instituted strict regulatory requirements for labeling and traceability and has effectively placed a moratorium on approving new crops. These regulations have caused friction with the U.S. government by limiting the import of U.S. agricultural products, many of which are genetically modified and none of which are required to carry labeling. The American Farm Bureau Federation estimates that U.S. corn producers alone would be able to export $300 billion more corn if the ban were lifted.
Genetic modification of foods is an area of biotechnology that is developing very rapidly, with many potential applications for improving the quantity and quality of the food supply. As with any new food technology, however, the safety of the products derived from this technology must be carefully assessed. Consumer concerns will likely continue to fuel the debate.
see also Biotechnology; Food Safety; Functional Foods; Pesticides.
M. Elizabeth Kunkel Barbara H. D. Luccia
Institute of Food Technologists (2000). "Genetically Modified Organisms: A Backgrounder." Food Technology 54:42–45.
International Food Information Council (2000). Food Biotechnology: A Communications Guide to Improving Understanding. Washington, DC: Author.
Food and Agriculture Organization of the United Nations (2000). "FAO Statement on Biotechnology." Available from <http://www.fao.org/biotech>
United States Department of Agriculture (2002). "Agricultural Biotechnology." Available from <http://www.usda.gov/agencies>
World Health Organization (2002). "Foods Derived from Modern Biotechnology." Available from <http://www.who.int>
"Genetically Modified Foods." Nutrition and Well-Being A to Z. . Encyclopedia.com. (April 29, 2017). http://www.encyclopedia.com/food/news-wires-white-papers-and-books/genetically-modified-foods
"Genetically Modified Foods." Nutrition and Well-Being A to Z. . Retrieved April 29, 2017 from Encyclopedia.com: http://www.encyclopedia.com/food/news-wires-white-papers-and-books/genetically-modified-foods
Genetically Modified Foods
Genetically Modified Foods
A genetically modified (GM) food is a plant that has a genetic change in each of its cells that a researcher has introduced. The modification may add a gene from a different species and thereby create a transgenic plant, or it may overexpress or silence a preexisting plant gene. Overexpression is accomplished by altering the promoter region of a gene, which controls how rapidly and in which cells the encoded protein is synthesized, thus directing a plant to manufacture more of a natural product. Conversely, a gene may be "silenced" (directed not to synthesize a protein) through the use of antisense technology, which applies a complementary nucleic acid to messenger RNA, halting expression of the encoded protein.
Genetic Modification in Animals and Plants
Animals have not yet been genetically modified to provide foods. Transgenic animals can, however, produce certain pharmaceuticals, but this approach is still experimental. One possible future use of transgenic animals is to create herds of cattle or sheep that are genetically resistant to developing transmissible spongiform encephalopathies, such as scrapie in sheep and "mad cow disease" in cattle.
Genetic modification in plants produces the same types of changes that result from traditional agricultural techniques, such as controlled breeding. However, genetic modification alters one gene at a time in a controlled manner, and typically has faster results than breeding plants with particular combinations of traits. With standard breeding techniques, it may take a generation to introduce, or remove, a single gene. Breeding a polygenic trait (a trait that involves more than one gene) into apples, which have a generation time of four years, could take two decades or longer.
GM traits that have already been introduced into plants include resistance to insects, insecticides, and herbicides; larger fruits; salt tolerance; slowed ripening; additional nutrients; easier processing; insecticide production; and the ability to take its own nitrogen from the air, lowering reliance on fertilizer. Specific products of genetic manipulation include insect-resistant corn, frost-resistant strawberries, rice that makes beta-carotene (a vitamin precursor ), frost and salt-tolerant tomatoes, delayed-ripening pineapples and bananas, canola with a healthier oil profile, and cotton and trees altered to make it easier to process fabric and paper. Some transgenic combinations are strange. Macintosh apples that have been given a gene from a Cecropia moth that encodes an antimicrobial protein, for example, are resistant to a bacterial infection called fire blight.
Whether a new variety of crop plant presents a hazard to human health depends upon the nature of the trait, not how the plant received that trait. For example, the U.S. Department of Agriculture found that a variety of potato obtained through conventional breeding was very toxic, and so it was never developed as a food. However, a potato developed through genetic modification at about the same time did not contain the toxin and was apparently safe to eat. This is why U.S. government regulatory agencies do not evaluate crops on how they were developed, but on their effects on the digestive tracts of animals.
Even after government agencies approve the marketing of a GM crop, consumer acceptance is crucial to its success. The FlavrSavr tomato, for example, was introduced in the 1980s. It ripened later, while in the supermarket, which extended its shelf life while providing an attractive product. However, the developers had focused only on this characteristic, and the tomatoes just did not taste very good. Consumer objection to GM foods also contributed to the FlavrSavr's failure. However, a high-solids GM tomato sold in England before the anti-GM movement began was popular with consumers, largely because it was priced lower than other tomatoes.
The Technique of Genetic Modification
The first step in developing a transgenic plant is to identify a trait in one type of organism that would make a useful characteristic if transferred to the experimental plant. The components of an experiment to create a transgenic plant are the gene of interest, a piece of "vector" DNA that delivers the gene of interest, and a recipient plant cell. Donor genes are often derived from bacteria, and are chosen because they are expected to confer a useful characteristic, such as resistance to a pest or pesticide.
To begin, the donor DNA and vector DNA are cut with the same restriction enzyme . This creates hanging ends that are the same sequence on both of the DNA molecules. Some of the pieces of donor DNA are then joined with vector DNA, forming a recombinant DNA molecule. The vector then introduces the donor DNA into the recipient plant cell, and a new plant is grown.
For plants that have two seed leaves (dicots), a naturally occurring ring of DNA called a Ti plasmid is a commonly used vector. Dicots include sunflowers, tomatoes, cucumbers, squash, beans, tomatoes, potatoes, beets, and soybeans. For monocots, which have one seed leaf, Ti plasmids do not work as gene vectors. Instead, donor DNA is usually delivered as part of a disabled virus, or sent in with a jolt of electricity (electroporation) or with a "gene gun" (particle bombardment). The monocots include the major cereals (corn, wheat, rice, oats, millet, barley, and sorghum).
Transgenesis in plants is technically challenging because the transgene must penetrate the tough cell walls, which are not present in animal cells. Instead of modifying plant genes in the nucleus, a method called transplastomics alters genes in the chloroplast, which is a type of organelle called a plastid. Chloroplasts house the biochemical reactions of photosynthesis. Transplastomics can give high yields of protein products, because cells have many chloroplasts, compared to one nucleus. Another advantage is that altered chloroplast genes are not released in pollen, and therefore cannot fertilize unaltered plants. However, it is difficult to deliver genes into chloroplasts, and expression of the trait is usually limited to leaves. This is obviously not very helpful in a plant whose fruits or tubers are eaten. The technique may be more valuable for introducing resistances than enhancing food qualities. Someday, transplastomics may be used to create "medicinal fruits" or edible vaccines.
GM beyond the Laboratory
After genetic modification, the valuable trait must be bred into an agricultural variety. Consider "golden rice," a grain that was given genes from daffodils and a bacterium to confer on it the ability to manufacture beta-carotene, a precursor to vitamin A. The first golden rice plants were created solely to show that the manipulation worked, and the modification of an entire biochemical pathway took a decade. The plant varieties were not edible, and the production of beta-carotene was low. In early 2002, however, researchers at the International Rice Research Institute in the Philippines began using conventional breeding to transfer the ability to produce beta-carotene from the inedible golden rice into edible varieties.
Genetic manipulation of plants can also focus on a particular species' own genes. This is the case for the potato, which has traditionally been difficult to cultivate because edible varieties must have an acceptable taste and texture, yet lack the alkaloid toxins that many natural strains produce. Breeding for so many characteristics is very time-consuming, and this is where genetic manipulation might speed the process. Researchers have identified a group of disease resistance genes on a region of one potato chromosome. The genes provide resistances to various insects, nematode worms, viruses, and Phytophthora infestans, which caused the blight infection that resulted in the nineteenth-century Irish potato famine. Being able to manipulate and transfer these genes will help researchers quickly breed safe and tasty new potato varieties, and perhaps transfer the potato's valuable resistance genes to related plants, such as tomatoes, peppers, and eggplants.
GM crops are widely grown in some countries, but are boycotted in others where many people object to genetic manipulation. As of 2001, 75 percent of all food crops grown in the United States were genetically modified, including 80 percent of soybeans, 68 percent of cotton, and 26 percent of corn crops. Farmers find that GM crops are cheaper to grow because their reliance on pesticides and fertilizer is less and a uniform crop is easier to harvest. Heavy reliance on the same varieties may be dangerous, however, if an environmental condition or disease should arise that targets the variety, but this dilemma also arises in traditional agriculture.
Because GM crop use is so pervasive in the United States, and because regulatory agencies evaluate the chemical composition and biological effects of crops rather than their origin, a consumer would not know that a fruit or vegetable has been genetically modified unless it is so labeled. Some people argue that these practices prevent consumers from having a choice of whether or not to use a genetically modified food.
see also Agricultural Biotechnology; Antisense Nucleotides; Plant Genetic Engineer; Prion; Restriction Enzymes; Transgenic Organisms: Ethical Issues; Transgenic Plants.
Fletcher, Liz. "GM Crops Are No Panacea for Poverty." Nature Biotechnology 19, no. 9 (September 2001): 797-798.
Hileman, Bette. "Engineered Corn Poses Small Risk." Chemical and Engineering News 79, no. 38 (September 17, 2001): 11.
Maliga, Pat. "Plastid Engineering Bears Fruit." Nature Biotechnology 19, no. 9 (September 2001): 826-927.
Potrykus, I. "Golden Rice and Beyond." Plant Physiology 123 (March 2001): 1157-1161.
"Genetically Modified Foods." Genetics. . Encyclopedia.com. (April 29, 2017). http://www.encyclopedia.com/medicine/medical-magazines/genetically-modified-foods
"Genetically Modified Foods." Genetics. . Retrieved April 29, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/medical-magazines/genetically-modified-foods
Genetically Engineered Foods
Genetically Engineered Foods
Through genetic engineering, scientists are able to alter, add, or remove specific genes from animals. Scientists are even able to add genes from a plant or animal to another plant or animal. The new genetic material in the plant or animal creates what is called a transgenic organism. A transgenic organism is one that contains genetic material from two different organisms.
Genetic engineering is attractive to agriculture because transgenic organisms can be designed with specific characteristics. Transgenic animals may grow faster, produce different proteins, resist disease, eat different foods, or gain weight faster. Transgenic plants may resist freezing, tolerate droughts or excess water, grow in poor soil conditions, resist pests, and resist pesticides. Transgenic plants or animals hold the promise of increasing production with less work and expense. While transgenic organisms may be the key to feeding the rapidly expanding human population, there are potential risks. Eating foods from transgenic organisms may cause allergic reactions or other interactions. Genes from transgenic organisms may find their way into "wild" populations of plants or animals, thereby affecting the genes of that population.
The first genetically engineered food introduced to the market was the Flavr Savr tomato in 1994. The Flavr Savr tomato was not a transgenic organism because new genetic material was not added. Instead, one of the genes in the tomato was altered to slow down the ripening process. The Flavr Savr tomato was engineered to ripen after being picked green and to slow down the chemical reactions that cause spoiling. The result was a tomato that can be picked green, ripen on the shelf on the way to the grocery store, and then remain fresh on the shelf. This type of genetically engineered food is probably safe because no new genetic material was inserted into the tomato plant.
Foods based on transgenic organisms have a higher risk for problems. In 1996 scientists created a transgenic soybean plant which had been altered to include a gene from the Brazil nut to increase its nutritional content. However, it was found that the soybeans from this transgenic plant produced some of the same proteins as Brazil nuts. One of these proteins was one to which some people are allergic. As a result, someone with allergies to Brazil nuts would also have an allergic reaction to the soybeans.
Not all transgenic organisms cause trouble. One of the first food uses for transgenic organisms was in the production of cheese. Cheese is made from milk. One of the first steps in making cheese is to separate the milk into curds (solids) and whey (liquid). This is done with an enzyme called rennin. Rennin has traditionally been extracted from the stomachs of slaughtered cows. In 1990, scientists used genetic engineering to splice the gene from cows that stimulated the production of rennin into yeast cells. The result was yeast cells that produce rennin. The rennin produced by the yeast cells is identical to the rennin produced by cows. The only difference is that the rennin from the yeast cells does not need to be extracted. This has lowered the price and increased the amount of rennin available. As a result, cheese is easier and cheaper to make. Transgenic rennin was approved for use in 1990; there have been no reports of problems and its use continues in about 65 percent of cheese production.
When genetically engineered organisms are used for food, it is easy to see where problems may develop. However, genetically engineered organisms could also pose problems with the environment. Crop pests such as insects damage a large percentage of crops each year. To combat pests, farmers use chemical pesticides. Sometimes these pesticides can cause problems with people who eat the crop or to animals living near the fields. Scientists have started using genetic engineering to make plants that resist crop pests. One way of making corn pest resistant is by inserting a gene from a bacterium, Bacillus thuringiensis. The resulting transgenic plant then produces a toxin originally produced by the bacteria. This toxin, Bt toxin, is poisonous to the corn borer, a common pest insect. Now, the corn plant itself produces its own pesticide. This means that farmers do not need to use pesticides on their fields, resulting in higher yields and fewer pesticides in the environment. At first glance, this seems like an excellent solution for increasing profits.
Unfortunately, corn borers, like other insects, reproduce quickly. Some of the corn borers were actually resistant to the Bt toxin. The corn borers that survived because of their resistance were able to pass the resistance on to their offspring. Now, just like with so many other pesticides, the pests were developing resistance. Scientists believed that this would be a minimal problem, and with limited use of other pesticides, these insects could be controlled. However, when farmers started growing transgenic corn that produced Bt toxin, they found an unexpected result.
Corn reproduces by pollen being carried from one plant to another. Unlike many plants, corn pollen is carried by the wind. Cornfields produce incredible amounts of pollen and the pollen often coats everything surrounding the fields. Scientists soon discovered that caterpillars of Monarch butterflies were being killed. The caterpillars eat a plant called milkweed, not corn plants. However, the transgenic corn pollen was deposited on the milkweed and the caterpillars were eating it along with the milkweed. The Bt toxin in the pollen was enough to kill the caterpillars.
Because of the benefits that genetically modified organisms provide, their use will probably continue to grow. No one knows how widespread the use of genetically modified organisms is in the United States. In 2000, the amount of transgenic crops was 52 percent of soybeans, 19 percent of corn, and 48 percent of cotton. The U.S. Food and Drug Administration has been working with scientists to devise ways of testing and even labeling foods that are transgenic or are derived from transgenic materials. The debate over genetically engineered foods and products will no doubt continue.
see also Bioethics; Farming; Genes; Genetic Engineering; Genetics.
Allan B. Cobb
Cobb, Allan B. Scientifically Engineered Foods: The Debate Over What's On Your Plate. Rosen Publishing Group, 2000.
Marshall, Elizabeth L. Hight-Tech Harvest: A Look at Genetically Engineered Foods. Danbury, CT: Franklin Watts, 1999.
Silver, Lee M. Remaking Eden: How Genetic Engineering and Cloning Will Transform the American Family. New York: Avon Books, 1998.
"Genetically Engineered Foods." Animal Sciences. . Encyclopedia.com. (April 29, 2017). http://www.encyclopedia.com/science/news-wires-white-papers-and-books/genetically-engineered-foods
"Genetically Engineered Foods." Animal Sciences. . Retrieved April 29, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/news-wires-white-papers-and-books/genetically-engineered-foods