Genetic engineering involves altering the genetic structure of embryonic cells or vectors to provide them with desired traits or to eliminate undesirable traits.
For thousands of years, humans have engaged in primitive forms of genetic engineering. They have chosen plants or animals with survival strength and desirable characteristics for further breeding, and have combined different strains of a species in attempts to retain and emphasize desirable characteristics of both. But in the 1970s, the field of genetic engineering took a quantum technologic leap when researchers developed a technique known as recombinant DNA, or gene splicing, enabling them to directly alter the genetic code and sequence of cells. This development transformed genetic engineering
Genes, which are composed of molecules of DNA, determine the physical characteristics that make organisms unique. Gene splicing, which involves introducing new genes into an organism in order to produce new characteristics, is performed in a number of ways. Sometimes a DNA "gun" is used to shoot genes directly into cells such as plant cells. When a gene cannot be directly "cut and pasted" from one organism to another, it may be placed in a harmless bacterium that duplicates repeatedly, acting as a "gene factory." The bacteria are then used to ferry the genes into cells.
A sheep named Dolly, born in 1997, was produced using a genetic engineering technique known as cloning. Here, scientists replaced the genetic material from one ewe's egg with genetic material from another ewe, producing an animal genetically unrelated to its surrogate mother. Hundreds of animals have been cloned, including bulls, cows, mice, monkeys, and pigs. Even clones of clones have been produced. Cloning is used to produce laboratory test animals with specific disease-related characteristics. Areas of cloning research range from cloning cows and sheep to produce medicines in their milk, to using cloning to preserve endangered species such as the Indian cheetah and the Asian guar.
Genetic engineering techniques are used to produce several widely used drugs. In addition to the hormone insulin, used to treat some forms of diabetes, these techniques are now used to produce the following: interferon, an antiviral and anticancer drug; tissue plasminogen activator (tPA), which dissolves blood clots; erythropoetin, which stimulates red blood-cell production; a hepatitis B vaccine; and others. In food production, genetic engineering can produce tomatoes with a longer shelf life; as well as crops with insect, herbicide, frost, and virus resistance. It is used to increase milk production in dairy cows, and to increase the size and infection-resistance of farmed fish like salmon. In addition, genetically altered bacteria have been used to decompose garbage and petroleum products.
Despite all its advances, the field of genetic engineering is still in its infancy. Now that researchers have mapped much of the human genome (or DNA blueprint), and some of the genes and their mutations responsible for genetic disorders like cystic fibrosis have been found, the next challenge is to understand proteins. These are the most complex of all known molecules. Each of the body's genes carries the code to create many different proteins (peptides), which are essentially the workers that carry out the DNA instructions. Understanding how messenger
proteins work is essential to preventing or curing disease. This will be a major focus of research over the next decade.
Promising areas of genetic engineering include human gene therapy and stem-cell research. Gene therapy involves repairing or replacing mutated genes in order to correct the malfunctions in protein production that can lead to disease. The use of gene therapy is being researched for diseases such as cancer, muscular dystrophy, hemophilia B, heart disease, and severe combined immune deficiency disease (known as "bubble boy disease"), among others. Stem cells are the undifferentiated cells from which specialized embryonic cells develop. They are considered one of science's best hopes for curing disease. Modified stem cells may one day be used to replace diseased cells affecting function throughout the body's systems. These cells also play an important role in tissue engineering, which involves the manufacture of blood products; artificial skin products; and biogenetic
replacement of organs, blood vessels, and cartilage. Other examples of genetic engineering research range from the manufacture of bananas engineered to contain vaccines (to eliminate the challenge of cold vaccine storage in developing countries) to coffee plants that have been altered to "switch off" caffeine before the beans even start growing.
Genetic engineering is controversial and has led to many protests regarding the potential of short- and long- term health and environmental risks. Stem-cell research is particularly controversial. Stem cells have traditionally been culled from aborted fetuses or from embryos left behind after successful fertility treatments, or they are produced using cloning technology. Many fear that using stem-cell research to cure genetic disorders or produce body tissues will eventually lead to the process being used to enhance or improve humans, a practice known as positive eugenics, termed by opponents as the "search for the master race." It is feared that altering human genomes may have unknown consequences for future generations that inherit the changes. Some individuals, including James Watson, co-discoverer of DNA's double-helix structure, are not opposed to altering DNA to make human "improvements."
The primary concerns with genetic engineering in plants are that a transferred gene could migrate unintentionally via pollen scattering from a transgenic plant to a related species and alter the ecosystem, or that a plant designed to kill a particular pest could end up killing beneficial insects like bees and butterflies. Transgenic plants could also interbreed with weeds, producing weeds resistant to herbicides. Allergens from one food crop, such as peanuts, can be transferred to another through genetic engineering. Animal-rights groups have argued that genetically engineered fish may cause problems if they interbreed with unaltered fish, which may change the characteristics of wild fish. The use of bovine growth hormone to increase dairy-cow milk production is also controversial, with critics questioning its safety for both cows and the humans who consume the milk.
The advances in genetic engineering require health care practitioners to consider their responsibilities in handling genetic information. As genetics advances are incorporated into tools for primary health care delivery, the use of genetic assessment testing will expand in medical practice. Health care practitioners, including nurses and allied-health professionals, will need a functional
Cloning—The production of an organism that is genetically identical to its parent.
Deoxyribonucleic acid (DNA)—The genetic material of all cellular organisms and most viruses. DNA carries the information needed to direct proteins. Each molecule of DNA consists of two twisted strands, called a double helix.
Eugenics—A practice involving use of genetic principles to "improve" humankind.
Gene—The basic unit of hereditary traits found in the cells of all living organisms, from bacteria to humans. Genes determine the physical characteristics that an organism inherits, such as hair and eye color.
Human Genome Project—An international scientific collaboration that seeks to identify and clarify the entire human genetic blueprint.
Protein—A molecule made of a sequence of amino acids. Proteins are the most common organic molecules in living organisms and among the most complex.
Recombinant DNA—DNA that has been altered by joining genetic material from two different sources. It usually involves putting a gene from one organism into the genome of a different organism.
Stem cells—The undifferentiated cells from which specialized embryonic cells develop.
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The American Society of Human Genetics. 9650 Rockville Pike, Bethesda, MD 20814-3998. (301)571-1825. <http://www.faseb.org/genetics/ashg/ashgmenu.htm>.
The International Society of Nurses in Genetics. <http://nursing.creighton.edu/isong>.
National Coalition for Health Professional Education in Genetics. (410) 583-0600. <http://www.nchpeg.org>.
The Human Genome Project. <http://www.ornl.gov/hgmis/medicine/medicine.html>.