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Introduction: What is Genetic Engineering?
Who would have thought that a tomato could possess characteristics of a fish? What about a plant possessing characteristics of a firefly; or a pig with human traits? These things may sound like science experiments gone wrong, but in truth, these are products of experiments that went well. The fish-like tomato and others are results of genetic modification or genetic manipulation, which are more commonly known as genetic engineering. Genetic engineering is the process of taking genes and segments of DNA from one species and putting them into another species, thus breaking the species barrier and artificially modifying the DNA of various species. These changes in DNA result in an alteration of reproductive and hereditary processes of the organisms since the process is irreversible and the organism's offspring will also possess this unique DNA (Levine).
The Process of Genetic Engineering
In order to understand how genetic manipulation is accomplished, it is important first to understand the structure of deoxyribonucleic acid, or DNA. Within its chemical structure, DNA stores the information that determines an organism's hereditary or genetic properties. DNA is made up of a linked series of units called nucleotides (Blaese), Different nucleotide sequences determine different genes genetic information. Genetic engineering is based on this genetic information.
Genetic manipulation is carried out through a process known as recombinant-DNA formation, or gene splicing. This procedure behind genetic engineering is one whereby segments of genetic material from one organism are transferred to another. The basis of the technique lies in the use of restriction enzymes that split DNA strands wherever certain desired secjuences of nucleotides, or specific genes, occur. This desired segment of DNA is referred to as donor DNA. The process of gene splicing results in a series of fragments of DNA, each of which express the same desired gene that can then combine with plasmids (Rubenstein).
Plasmids are small, circular molecules of DNA that are found in many bacteria. The bacteria act as vectors in the process of genetic engineering. The desired gene cannot be directly inserted into the recipient organism, or host, therefore there must be an organism that can carry the donor DNA into the host. Plasmid DNA is isolated from bacteria and its circular structure is broken by restriction enzymes (Dworkin). The desired donor DNA is then inserted in the plasmid, and the circle is resealed by ligases, which are enzymes that repair breaks in DNA strands. This reconstructed plasmid, which contains an extra gene, can be replaced in the bacteria, where it is cloned, or duplicated, in large numbers. The combined vector and donor DNA fragment constitute the recombinant-DNA molecule. Once inside a host cell, this molecule is replicated along with the host's DNA during cell division. These divisions produce a clone of identical cells, each having a copy of the recombinant-DNA molecule and thus permanently changing the genetic makeup of the host organism (Steinbrecher). Genetic engineering has been accomplished.
The Many Uses of Genetic Engineering
Are there any benefits that genetic engineering could bring to humankind? Actually, there are many. By performing genetic engineering, scientists can obtain knowledge about genetic mechanisms. For example, they may be able to uncover some secrets of genetic mapping. Genetic mapping is the identification of individual genes for various functions. If scientists are rising restriction enzymes to splice certain genes, they must be able to identify the genes. Thus, genetic engineering helps to identify certain nucleotide sequences, and to use various restriction enzymes to "read" the sequences. For example, if it appears that a single gene is responsible for a certain function, the recombinant-DNA process may tell us otherwise that two multiple genes, or even other factors are responsible for the specific function (Zhu).
Genetic manipulation is most commonly used to transfer desirable qualities from one organism to another to improve the ability of other species to serve humankind. Many examples of this lie in the use of genetic engineering to solve many problems with regards to food production and agriculture, waste disposal and industry, as well as disease and medicine (Rubenstein). The processes are also used for examining evolutionary processes (Levine).
Food Production and Agriculture
Dozens of food crops have now been genetically altered to enhance their qualities for the market or improve growing characteristics. Recombinant-DNA has been used to combat one of the greatest problems in plant food production: the destruction of crops by plant viruses as well as the weather. By transferring the protein-coat gene of the zucchini yellow mosaic virus to squash plants that had previously sustained great damage from the virus, scientists were able to create transgenic squash plants with immunity to this virus (Rubenstein).
Scientists have also developed transgenic bacteria that protect strawberry plants from injury by frost. The bacteria commonly found on strawberry plants secrete a protein that initiates the formation of ice crystals when the temperature falls to freezing (Rubenstein). In the genetically modified bacteria, the gene that codes for the protein has been deleted. In the absence of the protein, ice formation does not occur until the temperature falls well below the freezing point. Normally, such a deep drop in the temperature does not occur until after the harvest period has ended. The first field test of these genetically modified bacteria was conducted in 1987, on a plot of strawberry plants, and similar experiments on potatoes showed that the gene-spliced bacteria were effective in establishing themselves on the plants and, later in the season, in preventing ice formation during periods of light frost (Levine). Genetic engineering has been used in plants as well as in animals. In the livestock industry, for example, large amounts of a growth hormone found in cows have been obtained from genetically engineered bacteria. When treated with this hormone, dairy cows produce more milk, and beef cattle have leaner meat. Similarly, a genetically engineered pig hormone causes hogs to grow faster and decreases fat content in pork (Rubenstein).
Waste Disposal and Industry
Gene transfers also have been applied in the management of industrial wastes. Genetically altered bacteria can be used to decompose many forms of garbage and to break down petroleum products. For example, an 'oil-eating "nonnatural manmade microorganism" exists, and is used for cleaning up oil spills. Recombinant-DNA technology also can be used to monitor the breakdown of pollutants. For example, naphthalene, an environmental pollutant present in artificially manufactured soils, can be broken down by the bacterium Pseudomonas fluorescens. To monitor this process, scientists transferred a lightproducing enzyme called luciferase, found in the bacterium Vibrio fischeri, to the Pseudornonas fluorescens bacterium. The genetically altered Pseudomonas fluorescens bacterium produces light in proportion to the amount of its activity in breaking down the naphthalene, thus providing a way to monitor the efficiency of the process (Rubenstein).
Disease and Medicine
Genetic engineering has been used in the field of medicine for many purposes regarding the control and improvement of health. The process has been used to correct inherited genetic defects causing disease (gene therapy), to counter effects of genetic mutations, to produce various pharniaceutical products (Levine).
Gene therapy is the use of genetic engineering techniques in the treatment of a genetic disorder or chronic disease. In 1990, a four-year-old girl received genie therapy treatment for adenosine deaminase (ADA) deficiency, an ordinarily fatal inherited disease of the immune system. Because of this genetic defect, the girl was susceptible to recurrent life-threatening infections. Doctors removed white blood cells from the child's body, let the cells grow in the lab, used a genetically modified virus to carry a normal ADA gene into her inimune cells, and then infused the genetically modified blood cells back into the patient's bloodstream. The inserted ADA gene then programmed the cells to produce the missing ADA enzyme, which led to normal immune function iii those cells. This treatment temporarily helped her to develop resistance to infection, and must be repeated periodically (Donnelly).
Another important medical application of the recombinant- DNA procedure has been the production of vaccines against a number of diseases. Heretofore, vaccination against a disease has involved the injection of killed or weakened microorganisms into a person, with the subsequent production of antibodies by the individual's immune system. This procedure has always carried the risk of there being live, virulent pathogens in the vaccine because of some error in the vaccine-producing process (Donnelly).
Through the recombinant-DNA procedure, it is now possible to transfer the genes that stimulate antibody formation to a harmless microorganism and use it as a vaccine against the particular disease. Vaccines have been successfully created using the harmless cowpox virus, the herpes simplex type I virus (cold sores), the influenza virus, and the hepatitis B virus through gene splicing (Blaese).
Genetic engineering has also contributed several pharmaceutical products (besides vaccinations). Recombinant-DNA procedures involving bacteria and donor DNA fragments have led to the increased availability of such medically important substances as insulin, interferon, and growth hormone (Rubenstein). These substances were previously available only in limited quantities from their primary sources.
Insulin is a hormone produced in the pancreas that controls the absorption of glucose by cells. Diabetics lack the hormone or have decreased levels of it. Using recombinant-DNA techniques, scientists have created human insulin, which is artificially produced by gene-splicing methods in bacteria. Heretofore, diabetic patients relied solely on insulin derived from the pancreases of animals to control glucose levels (Levine).
The protein interferon is released into the bloodstream to induce healthy cells to manufacture an enzyme that counters a viral infection. It can also be effective against some forms of cancer, leukemia, genital warts, and the common cold. For many years, the supply of human interferon for research was limited by costly extraction techniques. l-Iowever, the protein became available in greater quantities through genetic engineering (Levine).
Evolution
Surprisingly, genetic engineering can also be used to uncover the past. Recombinant-DNA procedures have been used to study the genes of extinct animals. A zebra-like animal called the quagga, for example, became extinct in the '1 9~ century, but some quagga skins with underlying muscle tissues have been salt-preserved in museums. Enzymes were used to release DNA from these muscle cells, yielding DNA fragments representing parts of different genes. These fragments were transferred to the plasmids of bacteria, where they were replicated along with the bacterial DNA. They were then retrieved, analyzed, and compared to corresponding DNA segments of closely related living animals, revealing that the quagga DNA differs from its zebra counterpart by about 5 percent. This amount of difference indicates that the quagga and zebra shared a common ancestor. With appropriate modifications, it should be possible to use this technique to study genes from the bones and teeth of long-extinct animals, providing new insights into the evolutionary process (Levine).
The Dangers of Genetic Engineering
Even though it may seem as if genetic engineering has so many positive aspects, there are just as many negatives to counter. Genetic engineering is really a test tube science which may be prematurely applied. A gene studied under a closed system, a test tube with no outside influence on the conditions of the experiment, can only give results about what it does and how it behaves in that particular system. The experiment cannot tell what the role and behavior of donor DNA will be once it's in the host cell, which is likely to be a totally unrelated species that may be very different from the experimental environment (Steinbrecher). The insertion of a foreign gene might trigger new cellular activities or interrupt current ones. For example, genes can normally be exchanged between different species, but the frequency of these natural transfers is limited by their defense (immune) systems. The immune system serves to prevent invasion by harmful foreign genes, viruses, and other substances, so that particular species is able to maintain its characteristic traits and norma] metabolism (Rubenstein). Genetic engineering, may, in turn, disrupt and weaken the immune systems by introducing foreign substances into organisms that they won't be able to fight. No one really knows the overall effect of this (Levine).
Foreign genes trigger new cellular activities in the form of resistance. The vectors used in the genetic engineering process are often resistant to many drugs such as antibiotics. Injecting a drug-resisting vector into a new organism will result in a drug-resistant host organism. The resistance may not necessarily be only to drugs, as is the case with frost-resistant plants. Since genetic engineering is irreversible, this method allows these altered organisms to become widespread in nature (Steinbrecher).
Creating organisms that are resistant to anything they weren't initially unaffected by disturbs the evolutionary process of natural selection, or survival of the fittest. Putting such a desirable gene into an organism may give them an edge over another that would not normally exist. This whole idea of meddling with nature raises a question of religion and ethics (Rubenstein). What about "God;" Do we have the right to be playing the role of a higher being? In fact, genetic engineering raises countless more unanswered questions. Should animals be used in research? Do animals have "rights", as we think of "human rights?" How does genetic engineering of food affect religious and other groups with strong dietary laws, such as vegetarians? How great are the potential risks involved in releasing genetically modified organisms into the biosphere without knowing all the possible consequences?
Other dangers of genetic engineering include the following:
- New toxins and allergens in foods as well as other damaging effects on health caused by unnatural foods: The process of genetic engineering can thus introduce dangerous new allergens and toxins into foods that were previously naturally safe. Already, one genetically engineered soybean was found to cause serious allergic reactions, and bacteria genetically engineered to produce large amounts of the food supplement tryptophan have produced toxic contaminants that have killed 37 people and permanently disabled 1,500 more (Steinbrecher).
- The disturbance of ecological balance and the spread of diseases across species barriers: When genetic engineers insert a new gene into any organism, there are "position effects" which can lead to unpredictable changes in the pattern of genetic function. The protein product of the inserted gene may carry out unexpected reactions and produce potentially toxic products. There is also serious concern about the dangers of using genetically engineered viruses as vectors in the generation of transgenic plants and animals. This could destabilize the genome, and also possibly create new viruses, and thus dangerous new diseases (Rubenstein).
- Unnatural loss of bio-diversity in crops: Biotechnology companies claim that their manipulations are similar to natural genetic changes or traditional breeding techniques. However, the cross-species transfers being made, such as between fish and tomatoes, or between other unrelated species, would not happen in nature and may create new toxins, diseases and weaknesses (Rubenstein). Also consider the fact that organisms are "sharing" characteristics that are supposed to be unique to them. , For example in the fish-like tomato, a fish and a tomato are no longer unique. There is less diversity since they are now more similar, though unnaturally, than they initially were.
- The creation of herbicide-resistant weeds, resulting in increased pollution of food and water supply: More than 50% of the crops developed by biotechnology companies have been engineered to be resistant to herbicides. Use of herbicide-resistant crops will lead to a threefold increase in the use of herbicides, resulting in even greater pollution of our food and water with toxins (Rubenstein).
- Unexpected characteristics may appear in genetically altered organisms:One batch of genetically engineered young salmon were pale green instead of the normal brown color of young salmon and rather than turning pink on maturation, they remained green (Cummins).
- Artificially induced characteristics and inevitable side effects will be passed on to all subsequent generations and to other related organisms. Once released, they can never be recalled or contained. The consequences of this are incalculable (Levine). Even when genetically engineered fish have appeared normal, their descendants have been born with deformities such as grotesquely deformed heads and gill flaps, and change of color (Cummins).
Regulation of Genetic Engineering
Although numerous dangers of genetic engineering exist, they have been highly exaggerated. There is a great need to understand the genetic basis of all diseases, not just those to be errors of experiments. For genetic diseases, the solution lies in curing the defects rather than in managing with lifelong and often inadequate treatments. Vaccines have been developed through genetic engineering and have virtually eliminated some of mans most dreaded diseases. Even though vaccines do kill or maim a small number of those inoculated, the exaggeration of the downsides and possible dangers in these experiments diverts attention from the research needed to solve these problems and prevent others (Levine). The potential dangers of such research must be balanced against the actual tragedies caused by other sources.
In an effort to prevent worldwide epidemics and other problems as a result of genetic engineering, the National Institutes of Health (NIH) has established regulations, and has published safety guidelines to minimize the hazards of research (Steinbrecher). These guidelines have been gradually relaxed because such research was proven to be safe. In 1985, the NIH approved experimental guidelines for treatment in which genes are transplanted to correct hereditary defects in human beings (gene therapy). In 1987, a committee of the National Academy of Sciences concluded that transferring genes between species of organisms posed no serious environmental hazards (Rubenstein).
Conclusion
Genetic engineering is a complicated process that can be used for many things from modifying organisms such as plants to serve humankind better, to developing helpful pharmaceutical products, and even providing clues to the evolutionary process (Levine). Despite the fact that the genetic manipulation process seems to result in more damage than help, these views are often exaggerated. Although no one can predict the future of any field of human endeavor, genetic engineering appears to be a feasible mechanism through which many problems of modern society can be solved.
References
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