Engineering Organisms (Genetics & Inherited Conditions)
Domestication and selective breeding of animals and plants began before recorded history. In fact, historians propose, the shaping of organisms to fit human needs contributed to the rise of settled complex cultures. Until late in the twentieth century, farmers and scientists could breed novel strains only from closely related species or subspecies because the DNA had to be compatible in order to produce offspring that in turn were fertile.
In the late 1970’s and early 1980’s, molecular biologists learned how to surpass the limitations of selective breeding. They invented procedures for combining the DNA of species as distantly related as microbes, plants, and animals. These organisms carrying the novel heritable genetic material derived from different species using recombinant molecular biology techniques are termed as transgenic or genetically modified organisms (GMO). Genetic engineering makes it possible to design novel organisms for genetic and biochemical research and for medical, agricultural, and ecological innovations. However commercial use of transgenic organisms created worldwide controversy because of their potential threat to human health and the environment.
Transgenesis seeks to produce an entirely modified organism by incorporating the transgene into all the cells of the mature organism and changing the genome. This is done by transforming not only the somatic (body) cells of the host...
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Transgenic AnimalsTransgenic organismsanimals (Genetics & Inherited Conditions)
In recent years the use of transgenic organisms has become widespread and a large variety of animals and plants has been successfully engineered. Some examples of transgenic mammals include mice, rabbits, pigs, sheep, and cows. Birds such as chickens as well as fishes like salmon and trout, and even amphibians like frogs and toads have been made transgenic. Among invertebrates, transgenic fruit flies (Drosophila melanogaster) and nematodes (Caenorhabditis elegans) have become indispensable for research.
The first transgenic mice were created by Rudolf Jaenisch in 1974, showing that SV40 viral DNA had integrated into mouse genome. In 1982, Richard Palmiter and Ralph Brinster created “supermice” that grew much larger than ordinary mice because these had received the rat growth hormone gene. Most of these transformations were generated by microinjection of DNA directly into cells. Later, scientists were able to deliver foreign genes into hosts by several other methods: incorporating them into retroviruses and then infecting target cells; electroinfusion, whereby an electric current passed the foreign DNA through the relatively flimsy animal cell wall; and biolistics, a means of mechanically shooting a DNA bullet into cells. Two methods, developed at first for mice, are particularly successful in creating genetically modified animals. The first entails injecting transformed...
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Transgenic PlantsTransgenic organismsplants (Genetics & Inherited Conditions)
Plant cells present greater difficulties for transformation because their cell walls are sturdier than animal cell walls. Microinjection and biolistics are possible, but tricky and slow. A breakthrough for plant transgenesis came in 1983, when three separate teams of scientists used plasmids as vectors (carrier molecules) to infect plants with foreign DNA. The achievement came about because of research into plant tumors caused by crown gall disease. The pathogen, the soil bacterium Agrobacterium tumefaciens, caused the disease by ferrying bits of its own DNA into the genome of plants via plasmids, circular bits of extranuclear DNA. Scientists found that they could take the same plasmid, cut out bits of its DNA with enzymes and insert transgenes, and then use the altered plasmids as vectors to transform plants. Subsequently, scientists discovered that liposomes can be vectors. A liposome is a tiny ball of lipids that binds readily to a cell wall, opens a passage, and delivers any DNA that has been put inside it.
A great variety of transgenic plants have been designed for agriculture to produce genetically modified (GM) foods. The first to be marketed was a strain of tomato that ripened slowly so that it gained flavor by staying longer on the vine and remained ripe longer on supermarket shelves. However this Flavr Savr tomato was not a commercial success. Other crops have been made resistant...
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The Debate over Transgenesis (Genetics & Inherited Conditions)
Transgenic organisms offer great benefits to humankind: deeper understanding of the genetic component in disease and aids in diagnosis; new, cheaper, more easily produced drugs; and crops that could help alleviate the growing hunger in the world. Yet during the 1990’s protests against transgenesis began that are as contentious as any since the controversy over the pesticide DDT during the 1960’s.
Some opponents object to the very fact that organisms are modified strictly for human benefit. They find such manipulations of life’s essential code blasphemous and arrogant, or at the very least unethical and reckless. Furthermore, animal rights groups regard the production of transgenic pharm and research animals as cruel and in violation of the natural rights of other species.
The greater portion of opponents, however, are concerned with specific dangers that transgenic organism may pose. Many consumers, most noticeably those in Europe, worry that GM foods contain hidden health risks. After transgenes were found to escape from crops and become part of wild plants, environmentalists proposed that there could be unforeseen and harmful ecological consequences, especially in the destruction of natural species and reduction of biodiversity.
Even those who welcome the creation of transgenic animals and plants are concerned about the legal and social effects. Principally, because biotechnology...
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Further Reading (Genetics & Inherited Conditions)
Brown, Kathryn, Karen Hopkin, and Sasha Nemecek. “GM Foods: Are They Safe?” Scientific American 284, no. 4 (2001): 52-57. Describes the risks and benefits in growing genetically modified foods and human consumption of them. Accompanied by graphics and tables that summarize and clarify technical matters.
Houdebine, Louis-Marie. “Production of Pharmaceutical Proteins by Transgenic Animals.” Comparative Immunology, Microbiology, and Infectious Diseases 32 (2009): 107–121. Explains the diverse range of trangenics available and the methods for production of biopharmaceutical products.
Lurquin, Paul F. The Green Phoenix: A History of Genetically Modified Plants. New York: Columbia University Press, 2001. Written by a pioneer in the field of transgenic plants, this technically detailed but readable book requires a basic familiarity with microbiology and genetics. The author discusses the ecological and ethical controversies with insight and balance.
Nicholl, Desmond S. T. An Introduction to Genetic Engineering. 2d ed. New York: Cambridge University Press, 2002. A thorough, lucidly structured survey of the techniques and applications of genetic engineering. One chapter is devoted to transgenic plants and animals.
Rehbinder, E., et al. Pharming: Promises and Risks of Biopharmaceuticals Derived from Genetically Modified Plants and Animals. Berlin:...
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Web Sites of Interest (Genetics & Inherited Conditions)
Council for Biotechnology Information. http://www.whybiotech.com. Presents information about the benefits and safety of agricultural biotechnology for the general public.
Human Genome Project Information: Genetically Modified Food and Organisms. http://www.ornl.gov/sci/techresources/Human_Genome/elsi/gmfood.shtml. A searchable professional database about lines of genetically modified animals, methods used to create them and descriptions of the modified DNA, the expression of transgenes, and how transgenes are named.
Information Systems for Biotechnology. http://www.isb.vt.edu/indexmain.cfm. Searchable database pertaining to the development, testing, and regulatory review of genetically modified plants, animals, and microorganisms within the United States and abroad.
International Service for Acquisition of Agri-Biotech Applications (ISAAA). http://www.isaaa.org/kc. A comprehensive searchable database addressing the use of biotechnology to benefit resource-poor farmers in developing countries. With links and a photo gallery.
University of Michigan: Transgenic Animal Model Core. http://www.med.umich.edu/tamc. A professional Web site for researchers seeking a host animal to test transgenes. However, it contains much useful general information about transgenics (especially transgenic rats), vectors, and laboratory...
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