Genetic modification is the manipulation of an organism's genes to introduce particular traits. All methods of breeding modify the genes, but the technique that is usually implied by the term "genetic modification," and that attracts the greatest deal of controversy, is DNA recombination - introducing genes from one species into another.
Methods of genetic modification
There are several methods to modify the genetic makeup of an organism. All important modern crops have been extensively modified by human action.
- Selective breeding is the oldest method, dating back around 12 000 years with ancient Israelites cultivating wheat and uses the same fundamental mechanism as natural evolution. The primary difference is that rather than happening through natural selection, breeding happens through artificial selection by humans. Examples include most animals and plants on a farm.
- Hybridization involves crossing two highly dissimilar strains of an organism with each other. Because most detrimental alleles are recessive, and are unlikely to occur in both strains, this results in organisms that suffer from very few genetic defects. The improved performance of wide crosses is referred to as heterosis or hybrid vigour. Examples include the sunflower and "brocoflower" (hybrid of broccoli and cauliflower) for plants, and the mule (horse and donkey) for animals. Hybrids are sometimes sterile.
- Doubled haploidy involves the action of the chemical colchicine, which interferes with meiosis and causes reproductive cells to contain two sets of chromosomes rather than one. This results in an organism in which all traits are homozygous. This crude modification can lead to a number of important effects, such as making a plant fertile after wide crossing.
- Mutation breeding involves subjecting organisms (usually plants) to chemical mutagens or ionizing radiation. This increases the rate of mutation, and therefore the chance of finding new interesting traits. Over 2500 registered varieties have been obtained through radiation breeding. Gawd was probably thinking this 4000 years ago with His cow genomes.Do You Believe That?
- In DNA recombination, the genetic code of an organism is directly modified by inserting foreign genes into its DNA, for example through a specially prepared virus or bacterial plasmid. This is the most precise and powerful method of genetic manipulation, and also the only one that attracts substantial controversy. Examples with bacteria of this would be E. coli strains with genes to make insulin, and Mycoplasma laboratorium, which had its genome completely designed by scientists.
Genetic modification has a wide range of applications. The most common genetically modified crops are designed to resist pests, herbicides, and changes in the environment; have an increased yield; have additional nutrients not found in "wild" foods; and/or stay fresh for longer periods after harvesting.
Other uses of genetic modification range from the production of insulin to the creation of a new lithium-ion battery, up to creating superheroes or, if otherwise inclined, your very own Legion of Terror.
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Genetic modification plays straight into what Isaac Asimov called "The Frankenstein Complex," where there is an irrational fear of those who "play God" by mucking with nature. Indeed, many opponents refer to GM food as "Frankenfood".
In a somewhat more rational manner, GM food opponents argue that global food shortages could be overcome by other methods such as better distribution and that genetic modification is done only to line the pockets of companies such as Monsanto. Monsanto sells seed for various GM crops developed to resist their (now out of patent) wide-spectrum herbicide glyphosate (RoundUp®); weeding is accomplished, then, by spraying growing fields with glyphosate. Of course, weeds are now developing resistance to ever-increasing levels of glyphosate.
Several concerns have been raised over GM foods:
- Concern over lack of "independent testing" of GM foods. Non-GM varieties are not tested at all, so even manufacturer testing is a substantial improvement.
- The rise in food allergies correlating to the rise of GM foods. All that can be said is correlation does not equal causation. The rise in allergies is a common phenomenon in developed countries, even though the popularity of GM food varies wildly between them.
- The impact on the environment where GM resistance leads to increased use of pesticides and herbicides. So far the evidence is mixed: some GM crops increase pesticide use, while other decrease it dramatically. In most cases where pesticide use increases, there is a shift to less toxic pesticides, so the environmental impact is nonetheless positive. The effect is also dependent on farming practices in the given area.
- What might happen if modified genes transfer laterally to other organisms. For example, herbicide resistance could transfer to related weedy species, producing herbicide resistant weeds - obviously an undesirable outcome. Occurrence of this gene flow has been confirmed in field studies, but so far it's uncertain whether this is a serious concern or not. It should be noted that herbicide and pesticide resistance is not a concern unique to GM crops.
- A common myth perpetrated by GM opponents is that the crops use "terminator seed" technology (technical name Genetic Use Restriction Technology, GURT) which causes the crops to yield sterile seeds. While testing has been conducted on GURT, and it could eliminate the transfer of GM traits to weedy species, there is actually a moratorium on its commercial use due to public opposition. Seed that cannot be saved for replanting is not unique to GM crops. Plants grown from traditional hybrid seed, in wide use since the 1920s, do not produce true copies in the second generation. Therefore, new seed must be bought every year from a plant breeder to keep its desirable characteristics.
So far, all evidence is overwhelmingly in favor of safety of GM foods for human consumption. Some even argue that the anti-scientific repression of GM foods by the environmental movement is the real problem. The environmental issues are more worthy of concern, in particular the possibility of herbicide-resistant GM crops to transfer the herbicide resistance trait into related wild or weedy species.
Human genetic engineering
The prospect of human genetic engineering has also been extremely controversial, less for health reasons and more out of ethical concerns. The practice does not now exist, but prenatal screening now allows parents to test a fetus or zygote for gender or disease. Critics point to a slippery slope, arguing that if parents can choose to only bear male children or rule out any children with a heightened risk of cancer, then it's likely that when technology allows they will also choose to bear only exceptionally intelligent children or those with other commonly-desired traits, such as blue eyes.
Movies such as the 1997 science fiction thriller Gattaca have conceived of a world rigidly stratified by genetic code, where the wealthy bear superhumans and a person's opportunities for advancement - as well as the concurrent creativity and growth of society - is limited to what's dictated by their genes. Surprisingly, this raises a good question that is as yet unanswered: does the diversity brought about by genetic variation and flaws outweigh the personal costs of parents' private tragedy?
- National Research Council's 2004 statement on the safety of genetically engineered foods.
- Scientific Facts on Genetically Modified Crops, Green Facts
- Tomorrow's Table
- ↑ http://en.wikipedia.org/wiki/Natufian_culture#Development_of_agriculture
- ↑ Edible Geography: Strange and Beautiful Seeds From the Atom
- ↑ Like frost-resistant strawberries.
- ↑ Like Golden Rice, which adds beta-carotene to normal rice to combat Vitamin A deficiencies in impoverished countries.
- ↑ Like the "Flavr-Savr" tomato.
- ↑ http://www.npr.org/templates/story/story.php?storyId=102647672
- ↑ http://www.innerself.com/Health/frankenfood.htm
- ↑ I'm a Starry-Eyed Techno-Utopian, PZ Myers
- ↑ http://www.mindfully.org/Pesticide/More-GMOs-Less-Pesticide.htm
- ↑ Watrud, L.S. et al., Evidence for landscape-level, pollen-mediated gene flow from genetically modified creeping bentgrass with CP4 EPSPS as a marker. Proceedings of the National Academy of Sciences, October 5, 2004, vol. 101, no. 40, pp. 14533-14538.
- ↑ GURT overview.
- ↑ http://aggie-horticulture.tamu.edu/archives/parsons/vegetables/seed.html
- ↑ Peer Reviewed Publications on the Safety of GM Foods
- ↑ Prospect Magazine: The real GM food scandal
- ↑ Gattaca, Internet Movie Database