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экология - Genetic Engineering
|Раздел: Рефераты >> экология|
All that we are is the result of what we have thought
For what shall it profit a man, if he shall gain
the whole world and lose his own soulThe Bible
While plant biotechnology has been used for centuries to enhance plants, microorganisms and animals for food, only recently has it allowed for the transfer of genes from one organism to another. Yet there is now a widespread controversy over the harmful and beneficial effects of genetic engineering to which, at this time, there seems to be no concrete solution. The ideas below are expected to bring in a bit of clearance into the topic. Here Im going to reveal some facts concerning genetic engineering, specially the technology, its weak and strong points (if any). Probably the information brought is a bit too prejudiced, for Im certainly not in favor of making jokes with nature, but I really tried to find some good things about GE.
What is genetic engineeringGenetic engineering is a laboratory technique used by scientists to change the DNA of living organisms.
DNA is the blueprint for the individuality of an organism. The organism relies upon the information stored in its DNA for the management of every biochemical process. The life, growth and unique features of the organism depend on its DNA. The segments of DNA which have been associated with specific features or functions of an organism are called genes.
Molecular biologists have discovered many enzymes which change the structure of DNA in living organisms. Some of these enzymes can cut and join strands of DNA. Using such enzymes, scientists learned to cut specific genes from DNA and to build customized DNA using these genes. They also learned about vectors, strands of DNA such as viruses, which can infect a cell and insert themselves into its DNA.
With this knowledge, scientists started to build vectors which incorporated genes of their choosing and used the new vectors to insert these genes into the DNA of living organisms. Genetic engineers believe they can improve the foods we eat by doing this. For example, tomatoes are sensitive to frost. This shortens their growing season. Fish, on the other hand, survive in very cold water. Scientists identified a particular gene which enables a flounder to resist cold and used the technology of genetic engineering to insert this 'anti-freeze' gene into a tomato. This makes it possible to extend the growing season of the tomato.
At first glance, this might look exciting to some people. Deeper consideration reveals serious dangers.
There are 4 types of genetic engineering which consist of recombinant engineering, microinjection, electro and chemical poration, and also bioballistics.
The first of the 4, recombinant engineering, is also known as r-DNA technology. This technology relies on biological vectors such as plasmids and viruses to carry foreign genes into cells. The plasmids are small circular pieces of genetic material found in bacteria that can cross species boundaries. These circular pieces can be broken, which results with an addition of a new genetic material to the broken plasmids. The plasmids, now joined with the new genetic material, can move across microbial cell boundaries and place the new genetic material next to the bacterium's own genes. After this takes place, the bacteria will then take up the gene and will begin to produce the protein for which the gene codes. In this technique, the viruses also act as vectors. They are infectious particles that contain genetic material to which a new gene can be added. Viruses carry the new gene into a recipient cell driving the process of infecting that cell. However, the viruses can be disabled so that when it carries a new gene into a cell, it cannot make the cell reproduce or make copies of the virus.
The next type of genetic engineering is referred to as microinjection. This technique does not rely on biological vectors, as does r-DNA. It is somewhat of a simple process. It is the injecting of genetic material containing the new gene into the recipient cell. Where the cell is large enough, injection can be done with a fine-tipped glass needle. The injected genes find the host cell genes and incorporate themselves among them.
Electro and chemical poration
This technique is a direct gene transfer involving creating pores or holes in the cell membrane to allow entry of the new genes. If it is done by bathing cells in solutions of special chemicals, then it is referred to as chemical poration. However, if it goes through subjecting cells to a weak electric current, it is called electroporation.
This last technique is a projectile method using metal slivers to deliver the genetic material to the interior of the cell. These small slivers, which must be smaller than the diameter of the target cell, are coated with genetic material. The coated slivers are propelled into the cells using a shotgun. After this has been done, a perforated metal plate stops the shell cartridge but still allows the slivers to pass through and into living cells on the other side. Once inside, the genetic material is transported to the nucleus where it is incorporated among host cells.
The history of GE
The concept was first introduced by an Australian monk named Gregor Mendel in the 19th century. His many experiments cemented a foundation for future scientists and for the founding concepts in the study of genetics.
Throughout Mendel's life, he was a victim of criticism and ridicule by his fellow monks for his "foolish" experiments. It took 35 years until he was recognized for his experiments and known for the selective breeding process. Mendel's discoveries made scientists wonder how information was transferred from parent to offspring and whether the information could be captured and/or manipulated.
James D. Watson and Francis H. C. Crick were curious scientists who later became known as the founding fathers of genetic engineering.
Watson and Crick wanted to determine how genetic blueprints are determined and they also proposed that DNA structures are genetic messengers or that chemical compounds of proteins and amino acids all come together as a way to rule out characteristics and traits. These 2 scientists produced a code of DNA and thus answered the question of how characteristics are determined. They also established that DNA are the building blocks of all organisms.
Selective breeding and genetic engineering
Selective breeding and genetic engineering are "both used for the improvement of human society." However, selective breeding is a much longer and more expensive process than genetic engineering. It takes genetic engineering only one generation of offspring to see and study improvement as opposed to selective breeding where many generations are necessary. Therefore, it
costs more to observe many generations.
Selective breeding is known as the natural way to engineer genes while genetic engineering is more advanced, technical, scientific, complex and is inevitable in out future.
What are the dangersMany previous technologies have proved to have adverse effects unexpected by their developers. DDT, for example, turned out to accumulate in fish and thin the shells of fish-eating birds like eagles and ospreys. And chlorofluorocarbons turned out to float into the upper atmosphere and destroy ozone, a chemical that shields the earth from dangerous radiation. What harmful effects might turn out to be associated with the use or release of genetically engineered organismsThis is not an easy question. Being able to answer it depends on understanding complex biological and ecological systems. So far, scientists know of no generic harms associated with genetically engineered organisms. For example, it is not true that all genetically engineered foods are toxic or that all released engineered organisms are likely to proliferate in the environment. But specific engineered organisms may be harmful by virtue of the novel gene combinations they possess. This means that the risks of genetically engineered organisms must be assessed case by case and that these risks can differ greatly from one gene-organism combination to another.
So far, scientists have identified a number of ways in which genetically engineered organisms could potentially adversely impact both human health and the environment. Once the potential harms are identified, the question becomes how likely are they to occur. The answer to this question falls into the arena of risk assessment.
In addition to posing risks of harm that we can envision and attempt to assess, genetic engineering may also pose risks that we simply do not know enough to identify. The recognition of this possibility does not by itself justify stopping the technology, but does put a substantial burden on those who wish to go forward to demonstrate benefits.
Fundamental Weaknesses of the Concept
Imprecise TechnologyA genetic engineer moves genes from one organism to another. A gene can be cut precisely from the DNA of an organism, but the insertion into the DNA of the target organism is basically random. As a consequence, there is a risk that it may disrupt the functioning of other genes essential to the life of that organism. (Bergelson 1998)
Side EffectsGenetic engineering is like performing heart surgery with a shovel. Scientists do not yet understand living systems completely enough to perform DNA surgery without creating mutations which could be harmful to the environment and our health. They are experimenting with very delicate, yet powerful forces of nature, without full knowledge of the repercussions. (Washington Times 1997)
Widespread Crop FailureGenetic engineers intend to profit by patenting genetically engineered seeds. This means that, when a farmer plants genetically engineered seeds, all the seeds have identical genetic structure. As a result, if a fungus, a virus, or a pest develops which can attack this particular crop, there could be widespread crop failure. (Robinson 1996)
Threatens Our Entire Food SupplyInsects, birds, and wind can carry genetically altered seeds into neighboring fields and beyond. Pollen from transgenic plants can cross-pollinate with genetically natural crops and wild relatives. All crops, organic and non-organic, are vulnerable to contamination from cross-pollinatation. (Emberlin 1999)
Here are the some examples of the potential adverse effects of genetically engineered organisms may have on human health. Most of these examples are associated with the growth and consumption of genetically engineered crops. Different risks would be associated with genetically engineered animals and, like the risks associated with plants, would depend largely on the new traits introduced into the organism.
New Allergens in the Food Supply
Transgenic crops could bring new allergens into foods that sensitive individuals would not know to avoid. An example is transferring the gene for one of the many allergenic proteins found in milk into vegetables like carrots. Mothers who know to avoid giving their sensitive children milk would not know to avoid giving them transgenic carrots containing milk proteins. The problem is unique to genetic engineering because it alone can transfer proteins across species boundaries into completely unrelated organisms.
Genetic engineering routinely moves proteins into the food supply from organisms that have never been consumed as foods. Some of those proteins could be food allergens, since virtually all known food allergens are proteins. Recent research substantiates concerns about genetic engineering rendering previously safe foods allergenic. A study by scientists at the University of Nebraska shows that soybeans genetically engineered to contain Brazil-nut proteins cause reactions in individuals allergic to Brazil nuts.
Scientists have limited ability to predict whether a particular protein will be a food allergen, if consumed by humans. The only sure way to determine whether protein will be an allergen is through experience. Thus importing proteins, particularly from nonfood sources, is a gamble with respect to their allergenicity.
Genetic engineering often uses genes for antibiotic resistance as "selectable markers." Early in the engineering process, these markers help select cells that have taken up foreign genes. Although they have no further use, the genes continue to be expressed in plant tissues. Most genetically engineered plant foods carry fully functioning antibiotic-resistance genes.
The presence of antibiotic-resistance genes in foods could have two harmful effects. First, eating these foods could reduce the effectiveness of antibiotics to fight disease when these antibiotics are taken with meals. Antibiotic-resistance genes produce enzymes that can degrade antibiotics. If a tomato with an antibiotic-resistance gene is eaten at the same time as an antibiotic, it could destroy the antibiotic in the stomach.
Second, the resistance genes could be transferred to human or animal pathogens, making them impervious to antibiotics. If transfer were to occur, it could aggravate the already serious health problem of antibiotic-resistant disease organisms. Although unmediated transfers of genetic material from plants to bacteria are highly unlikely, any possibility that they may occur requires careful scrutiny in light of the seriousness of antibiotic resistance.
In addition, the widespread presence of antibiotic-resistance genes in engineered food suggests that as the number of genetically engineered products grows, the effects of antibiotic resistance should be analyzed cumulatively across the food supply.
Production of New Toxins
Many organisms have the ability to produce toxic substances. For plants, such substances help to defend stationary organisms from the many predators in their environment. In some cases, plants contain inactive pathways leading to toxic substances. Addition of new genetic material through genetic engineering could reactivate these inactive pathways or otherwise increase the levels of toxic substances within the plants. This could happen, for example, if the on/off signals associated with the introduced gene were located on the genome in places where they could turn on the previously inactive genes.
Concentration of Toxic Metals
Some of the new genes being added to crops can remove heavy metals like mercury from the soil and concentrate them in the plant tissue. The purpose of creating such crops is to make possible the use of municipal sludge as fertilizer. Sludge contains useful plant nutrients, but often cannot be used as fertilizer because it is contaminated with toxic heavy metals. The idea is to engineer plants to remove and sequester those metals in inedible parts of plants. In a tomato, for example, the metals would be sequestered in the roots; in potatoes in the leaves. Turning on the genes in only some parts of the plants requires the use of genetic on/off switches that turn on only in specific tissues, like leaves.
Such products pose risks of contaminating foods with high levels of toxic metals if the on/off switches are not completely turned off in edible tissues. There are also environmental risks associated with the handling and disposal of the metal-contaminated parts of plants after harvesting.
Enhancement of the Environment for Toxic Fungi
Although for the most part health risks are the result of the genetic material newly added to organisms, it is also possible for the removal of genes and gene products to cause problems. For example, genetic engineering might be used to produce decaffeinated coffee beans by deleting or turning off genes associated with caffeine production. But caffeine helps protect coffee beans against fungi. Beans that are unable to produce caffeine might be coated with fungi, which can produce toxins. Fungal toxins, such as aflatoxin, are potent human toxins that can remain active through processes of food preparation.
No Long-Term Safety Testing
Genetic engineering uses material from organisms that have never been part of the human food supply to change the fundamental nature of the food we eat. Without long-term testing no one knows if these foods are safe.
Decreased Nutritional Value
Transgenic foods may mislead consumers with counterfeit freshness. A luscious-looking, bright red genetically engineered tomato could be several weeks old and of little nutritional worth.
Problems Cannot Be Traced
Without labels, our public health agencies are powerless to trace problems of any kind back to their source. The potential for tragedy is staggering.
Side Effects can Kill
37 people died, 1500 were partially paralyzed, and 5000 more were temporarily disabled by a syndrome that was finally linked to tryptophan made by genetically-engineered bacteria.
As with any new technology, the full set of risks associated with genetic engineering have almost certainly not been identified. The ability to imagine what might go wrong with a technology is limited by the currently incomplete understanding of physiology, genetics, and nutrition.
Potential Environmental Harms
One way of thinking generally about the environmental harm that genetically engineered plants might do is to consider that they might become weeds. Here, weeds means all plants in places where humans do not want them. The term covers everything from Johnson grass choking crops in fields to kudzu blanketing trees to melaleuca trees invading the Everglades. In each case, the plants are growing unaided by humans in places where they are having unwanted effects. In agriculture, weeds can severely inhibit crop yield. In unmanaged environments, like the Everglades, invading trees can displace natural flora and upset whole ecosystems.
Some weeds result from the accidental introduction of alien plants, but many were the result of purposeful introductions for agricultural and horticultural purposes. Some of the plants intentionally introduced into the United States that have become serious weeds are Johnson grass, multiflora rose, and kudzu. A new combination of traits produced as a result of genetic engineering might enable crops to thrive unaided in the environment in circumstances where they would then be considered new or worse weeds. One example would be a rice plant engineered to be salt-tolerant that escaped cultivation and invaded nearby marine estuaries.
Gene Transfer to Wild or Weedy Relatives
Novel genes placed in crops will not necessarily stay in agricultural fields. If relatives of the altered crops are growing near the field, the new gene can easily move via pollen into those plants. The new traits might confer on wild or weedy relatives of crop plants the ability to thrive in unwanted places, making them weeds as defined above. For example, a gene changing the oil composition of a crop might move into nearby weedy relatives in which the new oil composition would enable the seeds to survive the winter. Overwintering might allow the plant to become a weed or might intensify weedy properties it already possesses.
Change in Herbicide Use Patterns
Crops genetically engineered to be resistant to chemical herbicides are tightly linked to the use of particular chemical pesticides. Adoption of these crops could therefore lead to changes in the mix of chemical herbicides used across the country. To the extent that chemical herbicides differ in their environmental toxicity, these changing patterns could result in greater levels of environmental harm overall. In addition, widespread use of herbicide-tolerant crops could lead to the rapid evolution of resistance to herbicides in weeds, either as a result of increased exposure to the herbicide or as a result of the transfer of the herbicide trait to weedy relatives of crops. Again, since herbicides differ in their environmental harm, loss of some herbicides may be detrimental to the environment overall.
Squandering of Valuable Pest Susceptibility Genes
Many insects contain genes that render them susceptible to pesticides. Often these susceptibility genes predominate in natural populations of insects. These genes are a valuable natural resource because they allow pesticides to remain as effective pest-control tools. The more benign the pesticide, the more valuable the genes that make pests susceptible to it.
Certain genetically engineered crops threaten the continued susceptibility of pests to one of nature's most valuable pesticides: the Bacillus
thuringiensis or Bt toxin. These "Bt crops" are genetically engineered to contain a gene for the Bt toxin. Because the crops produce the toxin in most plant tissues throughout the life cycle of the plant, pests are constantly exposed to it. This continuous exposure selects for the rare resistance genes in the pest population and in time will render the Bt pesticide useless, unless specific measures are instituted to avoid the development of such resistance.
Addition of foreign genes to plants could also have serious consequences for wildlife in a number of circumstances. For example, engineering crop plants, such as tobacco or rice, to produce plastics or pharmaceuticals could endanger mice or deer who consume crop debris left in the fields after harvesting. Fish that have been engineered to contain metal-sequestering proteins (such fish have been suggested as living pollution clean-up devices) could be harmful if consumed by other fish or raccoons.
Creation of New or Worse Viruses
One of the most common applications of genetic engineering is the production of virus-tolerant crops. Such crops are produced by engineering components of viruses into the plant genomes. For reasons not well understood, plants producing viral components on their own are resistant to subsequent infection by those viruses. Such plants, however, pose other risks of creating new or worse viruses through two mechanisms: recombination and transcapsidation.
Recombination can occur between the plant-produced viral genes and closely related genes of incoming viruses. Such recombination may produce viruses that can infect a wider range of hosts or that may be more virulent than the parent viruses.
Transcapsidation involves the encapsulation of the genetic material of one virus by the plant-produced viral proteins. Such hybrid viruses could transfer viral genetic material to a new host plant that it could not otherwise infect. Except in rare circumstances, this would be a one-time-only effect, because the viral genetic material carries no genes for the foreign proteins within which it was encapsulated and would not be able to produce a second generation of hybrid viruses.
Gene Pollution Cannot Be Cleaned Up
Once genetically engineered organisms, bacteria and viruses are released into the environment it is impossible to contain or recall them.
Unlike chemical or nuclear contamination, negative effects are irreversible.
DNA is actually not well understood.
Yet the biotech companies have already planted millions of acres with genetically engineered crops, and they intend to engineer every crop in the world.
The concerns above arise from an appreciation of the fundamental role DNA plays in life, the gaps in our understanding of it, and the vast scale of application of the little we do know. Even the scientists in the Food and Drug administration have expressed concerns.
As with human health risks, it is unlikely that all potential harms to the environment have been identified. Each of the potential harms above is an answer to the question, "Well, what might go wrong" The answer to that question depends on how well scientists understand the organism and the environment into which it is released. At this point, biology and ecology are too poorly understood to be certain that question has been answered comprehensively.
Any prosCertainly, there should be some. Still, most of them are connected with commercial gains for genetic engineering companies. A popular claim, that farmers will benefit, is simply not true. It is just the same thing with consumers. No one is going to feed the poorest with GE products for the famine in many underdeveloped countries is simply the matter of inability to buy food, not lack of it. So today, at the present stage of development, we hardly need GE expanding on food products, needless to say about animal and human cloning. Incidentally, some daydreaming proponents of GE really believe that mankind will not be able to survive without it. According to them, we will certainly have to genetically upgrade ourselves in response to governmental activities. The humans will be able to hibernate just like some animals to cover long distances without aging, and, probably, will become immortal
Still, what about the present need of GEWhere can GE particularly be used now without a threat to the humans and the environmentSo, scientists say that genetic engineering can make it possible to battle disease (cancer, in particular), disfigurement, and other maladies through a series of medical breakthroughs that will be beneficial to the human race. Moreover, cloning will be able to end the extinction of many endangered species. The main question is whether we can trust genetic engineering. The fact is that even genetically changed corn is already killing species.
The recent research showed that pollen from genetically engineered corn plants is toxic to monarch butterflies. Corn plants produce huge quantities of pollen, which dusts the leaves of plants growing near corn fields. Close to half the monarch caterpillars that fed on milkweed leaves dusted with Bt corn pollen died. Surviving caterpillars were about half the size of caterpillars that fed on leaves dusted with pollen from non-engineered corn. Something is wrong with the engineered products they are different, so we cannot be sure about the effect they will bring about.
So, is the technology trustworthyI suppose not.
So, do we need itThere are far too many disadvantages of GE and far too many unpredictable things may happen. The humans are amateurs in this area, in fact, they are just like a monkey taught to press PC buttons. We have almost no experience, the technology has not yet evolved enough. I believe, we should wait, otherwise we may give birth to a trouble, which would be impossible to resolve.
1. David Heaf Pros and Cons of Genetic Engineering, 2000, ifgene;
2. Ricarda Steinbrecher, 'From Green to Gene Revolution', The Ecologist, Vol 26 No 6;
3. Genetic Engineering Kills Monarch Butterflies, Nature Magazine, May 19,1999;
4. Who's Afraid of Genetic EngineeringThe New York Times August 26, 1998;
5. Sara Chamberlain Techno-foods, August 19, 1999, The New Internationalist;
6. W French Anderson, 'Gene Therapy' in Scientific American, September 1995;
7. Nature Biotechnology Vol 14 May 1996;
8. Andrew Kimbrell 'Breaking the Law of Life' in Resurgence May/June 1997 Issue 182;
9. Jim Hightower Whats for dinner, May 29, 2000
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