GENETIC ENGINEERING: Redrawing the Blueprint of Life - 4. Designer Genes
Figure 1. A scientist in a French laboratory working on mapping the human genome.
Figure 2. The corn plants in this greenhouse have been genetically engineered to resist attack by a pest called the European corn borer.
Figure 3. This transgenic ewe has been give the human gene that causes the production of a protein called antitrypsin in the sheep's milk. Her lamb (in the foreground) is also transgenic for this protein.
Figure 4. Researchers have genetically improved tomatoes to reduce the production of a gas called ethene that causes tomatoes to ripen. When the gene is inserted into the tomato plant, it slows the ripening process. This allows the fruit to reach maturity on the plant, providing customers with vine-ripened tomatoes year-round.
One of the greatest scientific ventures of recent times has been the Human Genome Project (see Figure 1). Its goal, accomplished in 2003, was to map the position of every one of the 100,000 or so genes strung out along the 23 pairs of human chromosomes.
The Human Genome Project marked a great leap forward in our efforts to learn the causes of genetic disease. Because of it, scientists are now pinpointing which genes are responsible for many of the genetic disorders that afflict human beings. This information will be used by gene therapists to improve greatly the understanding of diseases such as cystic fibrosis, hemophilia, sickle-cell anemia (another blood disorder), and muscular dystrophy (a condition in which a person's muscles gradually waste away). Improved knowledge of the location of particular genes will help scientists develop better treatments and eventually, perhaps, find permanent cures for these diseases.
Along with the benefits that gene therapy may bring, however, there are dangers. In time, scientists may be able to make widespread changes to a person's DNA. Genetic engineering may even progress to the point where it becomes possible to design how a future human being will look.
Gene therapy and genetic engineering raise some important concerns. Few people would doubt the value of gene therapy that can cure a serious disease such as cystic fibrosis. But there is uncertainty over how much tampering should be allowed with an individual's genetic makeup. Should gene therapy, for instance, be used to correct minor genetic ailments like color blindness? Should it be used to ensure that people do not grow up with crooked teeth or flat feet?
If minor genetic conditions are eventually treated by gene therapy, people may be tempted to go a step further. Some parents may wish to use genetic engineering to select their baby's appearance.
Height, the color of eyes, hair, and skin, shoe size, muscle build, and many other physical characteristics are determined, in part, by the coded instructions in our genes. But should it be lawful to influence how a future human being will look by altering a child's genes before birth?
Like many developments in science, genetic engineering could be used in ways that are both good and bad for human beings. During the Second World War, Adolf Hitler and other members of Germany's ruling Nazi party sought to exterminate whole groups of people – such as Jews, homosexuals, Gypsies, and disabled people – whom they considered to have inferior genes. The Nazis' goal was to breed a new race of strong, white-skinned, fair-haired people who would rule over everyone else. If, in the future, other evil dictators like Hitler were to rise to power, they might try to use genetic engineering for their own ends.
Mighty Mouse and Beyond
Not surprisingly, many doctors would like to see governments around the world introduce strict rules to control the use of genetic engineering. These rules would prevent altered genes from being passed on to future generations – at least until the altered genes were proved to be safe. The regulations would also ensure that gene therapy was used only to cure diseases and not to help determine a person's appearance and other physical characteristics.
The laws governing genetic engineering on human beings are likely to be strict. However, scientists have already carried out wide-ranging experiments on animals and plants (see Figure 2). They have created TRANSGENC ANIMALS and plants by taking genes from one organism and placing them in the DNA of a different kind of creature.
In 1981, researchers took the gene for producing growth hormone in rats and injected it into the fertilized eggs of mice. Growth hormone is a chemical that controls how fast and how much an individual grows. The growth hormone gene from the rats made the injected mice grow to be half as big again as a normal mouse. However, the results of this type of experiment are hard to predict. For example, when the human growth hormone gene was put into the fertilized eggs of pigs, the pigs did not grow larger. Instead, they produced leaner meat and were cross-eyed.
There is much debate about whether experiments should be carried out on animals, particularly if the tests may cause any sort of suffering. Supporters of genetic experiments on animals, however, argue that it is only through research on other species that scientists can develop new forms of gene therapy for human beings.
Animals have been genetically engineered to produce important, rare drugs in their milk. These valuable medicines include insulin, which is needed by people who suffer from diabetes, and antitrypsin, a chemical that can help in the treatment of lung diseases.
To turn an animal into a kind of living drug factory, scientists extract, from a human cell, the gene for making the required substance. Then this gene is placed inside the nucleus of a fertilized egg of an animal, such as a sheep. As the young sheep develops, each of its cells will include a copy of the human gene. Finally, when the sheep has young of its own and produces milk, its milk will contain small amounts of the substance for which the human gene carries the code (see Figure 3).
Research is now being done to improve the quantity of various types of drugs produced in animals' milk. The yield of these drugs is expected to increase gradually. By the beginning of the twenty-first century, large stocks of animals such as sheep and cows may have been genetically engineered to produce everything from blood-clotting substances for hemophilia sufferers to human growth hormone.
Through genetic engineering, entirely new kinds of life-forms are being created. These include plants that make their own pesticides, bacteria that boost the fertility of the soil in which they live, and other kinds of bacteria that clean up pollution in oceans and rivers. By placing new genes into existing life-forms, scientists can in effect design creatures to suit specific human needs (see Figure 4).
Much good may come from setting genetically engineered organisms free into the environment. Already new kinds of GENETICALLY MODIFIED cereal crops, fruits, and vegetables that can resist disease and pests have been developed. Some plants are being designed that can produce their own insecticide. This will allow farmers to use less chemical spray. Eventually crops may be tailored to live in places where there is poor soil or very little rain.
But there are risks. Transgenic animals and plants are unknown in the natural world. No one can be sure what effect these genetically altered life-forms might have on other species. One danger is that a genetically engineered organism might be safe in itself but its altered genes might be transferred to other living things, which may be harmed. Another possibility is that by making plants resistant to some kinds of germs, we will encourage the evolution of other kinds of disease-causing germs.
In the United States, between 1974 and 1976, public concern was so great that all research into genetic engineering was stopped. Then a set of guidelines was introduced to control possible dangers. Most countries now have similar rules. The first release of genetically engineered organisms, in the form of pesticides, took place in the United States in 1985. Further releases took placed under controlled conditions to ensure that introducing transgenic animals and plants into the environment was done with the minimum of risk.
In 1994, the first genetically engineered produce went on sale in stores around the United States. This included tomatoes in which the genes had been altered so that the fruit would ripen without rotting. Meanwhile, environmentalists are urging extreme caution before such "unnatural" living things are let out of the laboratory.
|How to Sow Cress and Reap Plastic|
In the future, farmers may grow plastics as a crop. Genetic engineers in the United States have altered the genes in a plant known as thale cress so that it produces a natural and totally biodegradable plastic material called PHB.
The researchers took two genes from a kind of bacterium that makes PHB naturally and stores it in the same way that human store fat. Then they introduced these genes into the cells of a thale cress plant so that it could make its own PHB. One problem is that the altered cress tends to become sickly, perhaps because it uses up so much energy in the production of the plastic. A way around this may be to put the genes into other kinds of plants, such as sugar beets or potatoes, that make great quantities of energy-storing substances like sugar and starch. If further research is successful, the twenty-first century could see farmers reaping harvests of plastic and other substances alongside their fields of corn and cabbage.