Genetic Engineering

Genetic Engineering
困难 689

了解基因工程所需要的选择育种、杂交、DNA重组等技术

Genetic Engineering

Genetic engineering is the alteration of an organism's genetic, or hereditary, material to eliminate undesirable characteristics or to produce desirable new ones. Genetic engineering is used to increase plant and animal food production; to diagnose disease, improve medical treatment, and produce vaccines and other useful drugs; and to help dispose of industrial wastes. Included in genetic engineering techniques are the selective breeding of plants and animals, hybridization (reproduction between different strains or species), and recombinant deoxyribonucleic acid (DNA).

Selective Breeding

The first genetic engineering technique, still used today, was the selective breeding of plants and animals, usually for increased food production. In selective breeding, only those plants or animals with desirable characteristics are chosen for further breeding. Corn has been selectively bred for increased kernel size and number and for nutritional content for about 7,000 years. More recently, selective breeding of wheat and rice to produce higher yields has helped supply the world's ever-increasing need for food.

Cattle and pigs were first domesticated about 8,000 years ago and through selective breeding have become main sources of animal food for humans. Dogs and horses have been selectively bred for thousands of years for work and recreational purposes, resulting in more than 130 different dog breeds and 100 different horse breeds.

Hybridization

Hybridization (cross-breeding) may involve combining different strains of a species (that is, members of the same species with different characteristics) or members of different species in an effort to combine the most desirable characteristics of both. For at least 3,000 years, female horses have been bred with male donkeys to produce mules, and male horses have been bred with female donkeys to produce hinnies, for use as work animals.

Recombinant DNA

In recent decades, genetic engineering has been revolutionized by a technique known as recombinant DNA, or gene splicing, which scientists use to directly alter genetic material. Genes consist of segments of the molecule DNA. In recombinant DNA, one or more genes of an organism are introduced to a second organism. If the second organism incorporates the new DNA into its own genetic material, recombined DNA results. Specific genes direct an organism's characteristics through the formation of proteins such as enzymes and hormones. Proteins perform vital functions — for example, enzymes initiate many of the chemical reactions that take place within an organism, and hormones regulate various processes, such as growth, metabolism, and reproduction. The introduction of new genes into an organism using recombinant DNA technology essentially alters the characteristics of the organism by changing its protein makeup. In humans, recombinant DNA is the basis of gene therapy, in which genes within cells are manipulated in order to produce new proteins that change the function of the cells.

Patenting Recombinant DNA Products

It takes an average of seven to nine years and an investment of about $55 million to develop, test, and market a new genetically engineered product. Because of this great cost, companies have sought to patent the results of their discoveries. In 1980 the Patent and Trademark Office of the U.S. Department of Commerce issued its first patent on an organism that had been produced with recombinant DNA. The patent was for a so-called oil-eating bacterium that could be used in the bioremediation (cleaning up by natural means) of oil spills from ships and storage tanks. Since then, hundreds of patents have been granted for genetically altered bacteria, viruses, and plants. In 1988 the first patent was issued on a transgenic animal, a strain of laboratory mice whose cells were engineered to contain a cancer-predisposing gene. The mice are used to test low doses of suspected carcinogens, or cancer-causing substances, and to test the effectiveness of anticancer therapies.

Controversies

Public reaction to the use of recombinant DNA in genetic engineering has been mixed. The production of medicines through the use of genetically altered organisms has generally been welcomed. However, critics of recombinant DNA fear that the pathogenic, or disease-producing, organisms used in some recombinant DNA experiments might develop extremely infectious forms that could cause worldwide epidemics. In an effort to prevent such an occurrence, the National Institutes of Health (NIH) in the United States has established regulations restricting the types of recombinant DNA experiments that can be performed using such pathogens. In Canada, recombinant DNA products are regulated by various government departments, including Agriculture and Agri-Food Canada, Health Canada, Fisheries and Oceans Canada, and Environment Canada.

Animal rights groups have argued that the production of transgenic animals is harmful to other animals. Genetically engineered fish raise problems if they interbreed with other fish that have not been genetically altered. Some experts fear that this process may change the characteristics of wild fish in unpredictable ways. A related concern is that engineered fish may compete with wild fish for food and replace wild fish in some areas.

The use of genetically engineered bovine somatotropin (BST) to increase the milk yield of dairy cows is particularly controversial. Some critics question the safety of BST for both the cows that are injected with it and the humans who drink the resulting milk. In the United States, a large percentage of dairy cows are treated with BST, but in Canada, BST cannot legally be sold. Scientists at Health Canada rejected the legalization of BST in 1999 based on evidence that BST causes health problems for cows. In particular, the Canadian scientists found that BST increases a cow's likelihood of developing mastitis, or infection of the udder, and it also makes cows more susceptible to infertility and lameness. Nevertheless, the scientists consider the milk obtained from cows injected with BST to be safe for human consumption.

Transgenic plants also present controversial issues. Allergens can be transferred from one food crop to another through genetic engineering. In an attempt to increase the nutritional value of soybeans, a genetic engineering firm experimentally transferred into soybean plants a Brazil-nut gene that produces a nutritious protein. However, when a study found that the genetically engineered soybeans caused an allergic reaction in people sensitive to Brazil nuts, the project was canceled.

Environmentalists fear that the transgenic plants may interbreed with weeds, producing weeds with unwanted characteristics, such as resistance to herbicides. An example of such interbreeding has been demonstrated in experiments involving transgenic oilseed rape. Environmentalists also argue that, due to natural selection, insects quickly develop resistance to plants that have been engineered to incorporate biological pesticides.

Opponents of genetic engineering warn that the use of genetically modified food crops could result in unforeseen problems. They point to a 1999 study that found that genetically modified corn produced pollen that killed monarch butterfly caterpillars in the laboratory. Although the study results were preliminary, as a precaution the Environmental Protection Agency (EPA) established new regulations in January 2000 to reduce potential risks posed by the corn crop. Among the new rules, the EPA has asked farmers to plant unmodified corn crops around the edges of genetically engineered corn fields in order to create a buffer that may prevent toxic pollen from blowing into butterfly habitats.

Many European and developing nations have voiced concern about the health and environmental risks associated with imported genetically modified food crops from the United States and other countries. In early 2000, 130 nations devised the Protocol of Biosafety. Once ratified, the treaty will require exporting nations to notify importers when products contain genetically modified organisms, including seeds, food crops, cattle, and fruit trees.

Some critics object to the patenting of genetically altered organisms because it makes the organisms the property of particular companies. For example, Costa Rica has enacted laws to prohibit the patenting of genes of native Costa Rican species by drug companies in other countries. To date, no laws are in place in the United States and Canada regulating the use of cloning technology, and some people fear the prospect of human cloning. If this technology remains unregulated, critics fear that it will provide the ability to create an "improved" human being with characteristics predetermined according to a scientist's particular bias.

— Microsoft Encarta Encyclopedia 2002

讨论区

还可以输入500 个字
  • 字数:1330个
  • 易读度:困难
  • 来源:外教社 2016-06-28