Techno food: genetically modified crops cook up a sizzling debate. (Life/Tech Science: Genetic Engineering * Food Safety).
Today nearly 70 percent of processed foods sold in the U.S. contain ingredients that have been injected with foreign genes, hereditary information in cells that control an organism's growth. The lab technique, gene-splicing (see "How to put a vitamin in rice", below), lets scientists transplant genes from almost any organism into another: Fish genes can be woven into strawberries, virus genes slipped into bananas. Result: genetically-modified, or GM, foods.
Genetic engineering shows remarkable real-life potential: worm-proof corn or cancer-fighting tomatoes, for example. But GM foods have also ignited a firestorm of protest. Critics warn of unforeseen side effects: allergic reactions, environmental damage, and poisoned wildlife.
Do we know enough about genetic engineering to experiment with the world's food supply? Are scientists creating miracles or "frankenfoods"? Read the pros and cons fueling the GM-food debate--then make up your own mind.
You've probably been eating GM goods for years. They first hit supermarket in 1992, though you may not know it since they don't require a special label, or look and taste different than non-GM foods.
Worldwide, nearly 800 million people are starving or severely malnourished--and their plight will worsen as the world's population swells from nearly 6.2 billion to a projected 7.6 billion by 2021. To keep up with an exploding demand for food, farmers will have to produce twice as many crops in the next 20 years as have been grown in the last 10,000 years!
How can genetic engineering help? Scientists are creating seeds that yield more food, grow in deserts and salty water, and resist common weeds and insects. One example: Researchers have taken a gene from the Arctic flounder--a fish that thrives in icy waters--to increase the cold tolerance of tomato plants.
Critics worry that GM foods may diminish the world's food supply in the long run. One major problem: gene flow, which means that windblown or animal-carried GM pollen can contaminate nearby plants, like weeds, which can grow rampant.
Biologist Sarah Ward at Colorado State University is researching a type of GM wheat resistant to the commercial weed-killer Roundup. "The idea is to kill the weeds, not the wheat," Ward explains. "But the problem is that GM wheat can cross-pollinate [mate] with the closely related weed, jointed goat grass." The results could prove disastrous: If the weed incorporates GM wheat's pesticide-resistant gene into its own DNA, making it immune to Roundup, the weed could potentially overrun healthy wheat crops. "That thought makes farmers go white in the face," says Ward.
Work is underway to create foods with "built-in" medicines that thwart disease. For example, scientists at the Boyce Thompson Institute at Cornell University isolated genes from the hepatitis B virus, an infectious particle that causes deadly liver disease. Then they spliced the virus genes into a banana's DNA to create an edible vaccine, a medicine used to trigger the body's immune system to fight disease. "After you eat the banana your body produces antibodies [germ-fighting molecules] against the virus," Ward says. Typical vaccines are injected into the body with a needle, which is expensive in developing countries and, if unsterile, can spread deadly diseases like AIDS.
Researchers are also trying to create cooking oils with less saturated fat, soybean oil with high levels of vitamin E (essential for red blood-cell production), and strawberries loaded with a cancer-fighting chemical called ellagic acid.
A big downside to GM food: allergies, the body's overactive response to foreign substances. Millions of people live with allergic reactions to foods such as nuts, fish, and milk. An allergy attack can cause rashes, asthma, seizures, and in extreme cases, death. "With GM food, we're adding proteins [chemical compounds essential for body growth and repair] from a lot of organisms that we don't eat, like petunias and bacteria, which could spark unknown allergies," says Jane Rissler, staff scientist at the Union of Concerned Scientists. "And we can't trace the allergy source because GM food is not yet labeled."
In 1996, U.S. farmers sprayed crops with an estimated 806 million pounds of toxic chemicals that kill weeds, fungi, and insects, says the Environmental Protection Agency. The pesticides also leave toxic residues on plants, leech into the soil, and contaminate groundwater.
For example, the wormy European corn borer (Ostrinia nubilalis) destroys over $1 billion worth of corn crops annually. To combat the pest, scientists isolated genes from a soil bacterium called Bacillus thuringiensis (Bt), which produces a toxin, or poison, that kills insects. Researchers spliced Bt into a corn seed's DNA. When a worm munches on Bt corn, it ingests the bacterial toxin and dies within days. Bt toxin genes have also been spliced into potatoes and cotton plants. In 1998, Bt cotton alone slashed pesticide use by 450 tons (992,080 pounds).
Although Bt corn toxins are harmless to humans, conflicting evidence indicates they might be poisonous to wildlife, like the monarch butterfly. Millions of monarch larvae (infant insects) feed on milkweed leaves often dusted by GM pollen. In 1999, researchers at Cornell University fed monarch larvae milkweed leaves coated with high doses of Bt corn pollen. Within days, half the larvae died. However, recent field studies have shown that Bt corn is harmless to butterfly larvae.
Many scientists also worry plant-eating insects and weeds will develop resistance to Bt crops, creating "super-bugs" or indestructible weeds. Resistance occurs when an organism develops a beneficial mutation, a random genetic change that lets it overcome a survival challenge--like exposure to Bt poison. "Pests are very effective at overcoming whatever mechanism we use to control them," says biologist Martina McGoughlin at the University of California at Davis. "Technology has to try to constantly stay one step ahead."
How to put a vitamin in rice
Scientists genetically engineer golden rice to contain vitamin A, a dietary nutrient essential for healthy eyesight, Here's how they do it:
(1) Genes carrying vitamin A are isolated from daffodils and the bacteria Erwinia uredovora.
(2) The genes are inserted into plasmids, small rings of bacterial DNA, a double-stranded molecule that contains genes.
(3) In a petri dish, plasmids infect rice embryos and incorporate their vitamin A genes into the rice's DNA.
(4) The "transgenic" rice is mated with normal rice grains suited to a region's growing conditions.
Humans have been altering plant genes for nearly 10,000 years to yield more desirable traits, like larger seeds or sweeter fruit. How does traditional plant breeding differ from genetic engineering? In nature, plants transfer genes through pollen, dust-like particles that carry male sex cells to female sex cells. After fertilization, the resulting seed is an equal cross between thousands of parental genes. With genetic engineering, individual genes are artificially inserted into a plant, which. acquires the desired traits immediately.
But biologist Margaret Mellon of the Union of Concerned Scientists is concerned: "We're making combinations of genes that aren't found in nature" she says. "You just can't get an elephant to mate with a corn plant"
What's a taco without a crunchy corn shell? A safe meal--at least for the 51 people who claimed to have fallen ill last year after eating GM-corn products, including Taco Bell's corn shells. Twenty-eight reported symptoms of an allergic reaction: rash, troubled breathing, and in some cases, fainting.
An allergy is the body's excessive immune response to a foreign substance, in this case, the alleged substance was Starlink corn, a type of GM corn approved only for use in animal feed. It accidentally wound up in corn products destined for humans. Since the allergy attacks, makers of Starlink corn have shelled out millions of dollars to buy back 300 different products that contain Starlink corn.
But is the corn really to blame? No, says the Centers for Disease Control (CDC).Their scientists tested blood samples from 17 affected people for GM-corn antibodies, blood proteins that attach to foreign substances in the body.
Although the CDC confirmed the illnesses, they say Starlink corn wasn't to blame since the antibodies weren't found. Victim Grace Booth is not convinced: "Everything else I ate in the 72 hours before I got sick, I've eaten again with no problem," she says.
History/Biography: The "father of genetics," Austrian scientist Gregor Mendel (1822-84), bred pea plants to study their inherited characteristics. Research Mendel's life and work, then write a report on how his revolutionary ideas about genes were received by the scientific community and general public during his lifetime.
Did You Know?
* Last year, more than 100 million acres of farmland worldwide--nearly equal to 76 million football fields--were planted with GM crops: mostly cotton, corn, canola, and soybeans. Consumers spent $2.3 billion dollars on foods made from GM crops.
* In the past decade, researchers have found no evidence of "super-weeds"--weeds resistant to GM crops that overtake valuable cropland--according to a recent study in Nature.
* In Africa, nearly half of all harvested fruit and vegetables rot before reaching consumer markets. "Transgenic" produce could potentially use genes to slow down how fast fruit and veggies rot.
National Science Education Standards
Grades 5-8: reproduction and heredity * populations and ecosystems * populations, resources, and environments * risks and benefits * science and technology in society
Grades 9-12: the cell * the molecular basis of heredity * the interdependence of organisms * population growth * natural resources * science and technology in local, national, and global challenges
"Grains of Hope," by J. Madeleine Nash, Time, July 31, 2001.
Transgenic Crop: An Introduction and Resource Guide www.colostate.edulprograms/lifesciences/ TransgenicCrops
PBS "Harvest of Fear" Web site: www.pbs.org/wgbh/harvest
Directions: Answer the following questions in complete sentences.
1. Describe two ways that genetically modified (GM) crops may be beneficial and two ways they may be harmful.
2. How are traditionally bred plants different from genetically engineered plants?
3. Do you support GM foods? State your reasons why or why not.
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|Date:||Nov 26, 2001|
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