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Genetic testing

Image showing a woman's genes with one extra X chromosome

Image showing a woman's genes with one extra X chromosome

Credits:Wessex Reg. Genetics Centre, Wellcome Images.

Since the discovery of genes as the molecular basis of heredity, researchers have investigated how hereditary diseases show in genetic material. Scientists have for instance compared the DNA of a healthy person to that of a person with a hereditary disease to locate abnormalities caused by the deletion, insertion or replacement of a base in a gene.

In 1977, researchers Walter Gilbert and Frederick Sanger developed genetic sequencing which allowed scientists to determine the order of bases along a region of DNA. Since the 1980s, scientists have used "knockout" experiments on animals like mice to investigate genetic disorders. The DNA of a mouse is changed by radioactivity or chemicals, and the mouse and generations of its mutated offspring are observed. This has led to breakthroughs in the understanding of diseases like cancer.

Today, four main types of genetic testing are performed:

1. Carrier identification is used to determine whether a person carries a genetic problem which he or she may pass on to offspring even if that person does not have the disease him- or herself.

2. Prenatal diagnosis is performed on an unborn foetus using amniocentesis.

3. Newborn screening is performed immediately after birth, testing for conditions which can be treated effectively such as phenylketonuria, a genetic disorder which leads to an enzyme deficiency.

4. Late-onset-disorder testing can be used at any point in a person's life to determine whether he or she is likely to develop a condition later in life. These tests can for instance indicate increased cancer risks, or late-onset hereditary disorders like Huntington's disease.



Related links

Techniques and Technologies:


W Allstetter, J Angelo and T Day, The cutting edge: an encyclopedia of advanced technologies (Oxford: Oxford University Press, 2000).
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