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Instant Expert: GM Organisms
GM Organisms - Is GM the future? Learn more in our continually updated special report.
By far the most common genetically modified (GM) organisms are crop plants. But the technology has now been applied to almost all forms of life, from pets that glow under UV light to bacteria which form HIV-blocking "living condoms" and from pigs bearing spinach genes to goats that produce spider silk.
GM tomatoes, as puree, first appeared on British supermarket shelves in 1996 (a different fresh GM tomato first appeared in the US in 1994), but the consumer furore that surrounded GM technology did not erupt until February 1999. This was because a controversial study suggested that a few strains of GM potatoes might be toxic to laboratory rats. Those experiments, subsequently criticised by other experts, were carried out in Scotland by biochemist Arpad Pustzai.
What followed was a European anti-GM food campaign of near religious fervour. Spearheaded in the UK by environmental groups and some newspapers, the campaign would have far-reaching consequences. It culminated in an unofficial moratorium on the growth and import of GM crops in Europe and led to a trade dispute with the US.
GM crops are today very rare in Europe, strict labelling laws and regulations are in place for food (DNA bar codes), and public opinion towards the technology remains largely negative. Several UK government reports have offered qualified support for GM crops and produce, though they argue that the economic benefits of the technology are currently small. Some African nations have also opposed engineered crops, even to the point of rejecting international food aid containing them.
GM produce has been taken up with far less fuss in the US (where it does not have to be labelled), India, China, Canada, Argentina, Australia and elsewhere. However controversy over a type of GM corn - only approved for animal feed - which turned up in taco shells and other products stirred opinion in the US.
The human race has methodically improved crop plants through selective breeding for many thousands of years, but genetic engineering allows that time-consuming process to be accelerated and exotic traits from unrelated species to be introduced. But not everyone agrees this is represents progress.
The root of genetic engineering in crops lies in the 1977 discovery that soil bug Agrobacterium tumefaciens can be used as a tool to inject potentially useful foreign genes into plants. With the help of that microbe, and other gene-implantation technologies such as electroporation, and gene guns, geneticists have developed a multitude of new crop types.
Most of these are modified to be pest, disease or herbicide resistant, and include: soya, wheat, corn (maize), oilseed rape (canola), cotton, sugar beet, walnuts, potatoes, peanuts, squashes, tomatoes, tobacco, peas, sweet peppers, lettuce and onions, among others. The bacterial gene Bt is one of the most commonly inserted. It produces an insecticidal toxin that is harmless to people.
Supporters of GM technology argue that engineered crops - such as vitamin A-boosted golden rice or protein-enhanced potatoes - can improve nutrition, that drought- or salt-resistant varieties can flourish in poor conditions and stave off world hunger, and that insect-repelling crops protect the environment by minimising pesticide use.
Other plants have been engineered to improve flavour, increase shelf life, increase hardiness and to be allergen-free (see also: hay fever-free grass). Geneticists have even created a no-tears onion to banish culinary crying, and novel caffeine-free coffee plants.
Critics fear that what they call "Frankenstein foods" could have unforeseen, adverse health effects on consumers, producing toxic proteins (and allergens) or transferring antibiotic-resistance and other genes to human gut bacteria to damaging effect. But there has been little evidence to back up such risks so far.
More plausible threats are that modified crops could become insidious superweeds, or that they could accidentally breed with wild plants or other crops - genetically polluting the environment. This could be a potentially serious problem if "pharm" crops, engineered to produce pharmaceutical drugs, accidentally cross breed with food varieties (or seeds become mixed up).
Large numbers of field trials, carried out by the UK government and others, reveal that gene transfer does occur. One 2002 study showed that transgenes had spread from US to traditional maize varieties in Mexico. A 2004 study revealed that conventional varieties of major US food crops have also been widely contaminated. Another study proved that pollen from GM plants can be carried on the wind for tens of kilometres.
Many experts agree that insect-repelling plants will also speed the evolution of insecticide-resistant pests. Normal crops are often grown alongside transgenic ones as refuges for the pests, in an attempt to prevent their accelerated evolution into "superpests".
Environmentalists also argue that growing GM crops affects farmland biodiversity. Field trials to test for this have produced mixed results - some suggesting that GM crops actually boost biodiversity.
Genetic modification of crops may offer the largest potential benefits to developing nations. However, the growing globalisation of agriculture is a trend that worries some. Activists and disgruntled farmers worry that the agricultural biotech industry is encouraging reliance on their own-brand herbicide-resistant plants (Roundup Ready for example), which could create monopolies.
Companies such as Monsanto or Syngenta protect their GM seeds with patents. In one well-known legal case a Canadian farmer was successfully prosecuted for growing GM canola, though he claimed seed had accidentally blown on to his land.
Companies have also investigated technology protection systems. One type of TPS, dubbed the Terminator system by its critics, is a genetic trick that means GM crops fail to produce fertile seeds. This prevents the traditional practice of putting seeds aside from the crop to replant the following year, forcing farmers to buy new seed every year. However, some biotech companies have pledged not to use this technology, despite the fact it could be a useful tool in preventing genetic pollution.
A clever genetic variation on that theme, the Exorcist system, allows the production of fertile seeds, but with any foreign GM DNA spliced out and destroyed. The GM revolution has not been restricted to crops. A small number of farm and laboratory animals have also been modified.
These include: quick-to-mature GM salmon, endowed with an early growth spurt, GM cows that produce casein-enriched milk ideal for cheese making, pigs bearing spinach genes that produce lower-fat bacon, goats engineered to churn out spider silk in their milk and mice that produce healthy fish oils.