Gene Technology
Rapidly changing technology is improving the detection of genetic diseases, both before and after birth.
One effort currently under way, called the Human Genome Project, is the identification and mapping of all the genes on human chromosomes. The project is essentially complete, and the entire human genetic code has been mapped. The hope is that this information will allow better prediction of health risk and better approaches to therapy, tailored much more to each individual. However, concerns have been raised that this information might be used improperly to deny health insurance coverage to people at high risk of particular diseases.
Other efforts involve studying individual genes to learn more about specific diseases. There are several ways to produce enough copies of a gene to study. In a laboratory, the gene to be copied is usually spliced into pieces of DNA inside a bacterium. Each time the bacterium reproduces, it makes an exact copy of all its DNA, including the spliced gene. Bacteria multiply very rapidly, so billions of copies of the original gene can be produced in a very short time.
Another technique for copying DNA uses the polymerase chain reaction (PCR). A specific segment of DNA, such as a specific gene, can be copied (amplified) in a laboratory. Starting with one DNA molecule, at the end of 30 doublings (only a few hours later) about a billion copies will be produced.
A gene probe can be used to locate a specific gene in a particular chromosome. A gene that has been cloned or copied becomes a labeled probe when a radioactive atom is added to it. The probe will seek out its mirror-image segment of DNA and bind to it. The radioactive probe can then be detected by sophisticated photographic techniques. With gene probes, a number of diseases can be diagnosed before or after birth. In the future, gene probes will probably be used to test people for many major genetic diseases. However, not everyone who has the gene for a given disease will actually develop that disease.
A technique called the Southern blot test is widely used to identify DNA. DNA is extracted from the cells of a person being studied and is cut into precise fragments with a type of enzyme called a restriction endonuclease. The fragments are separated in a gel by a technique called electrophoresis, placed on filter paper, and covered with a labeled probe. Because the probe binds only to its mirror image, it identifies any DNA fragment matching the probe.
 See the sidebar And Then There Were Two.
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