duces large quantities of a DNA fragment without needing a living cell. Starting
with one small piece of DNA, PCR can make billions of copies in a few hours.
These large quantities of DNA can be easily analyzed.
PCR and DNA probes have been of great value to the areas of molecular biol-
ogy, medicine, and biotechnology. Using these tools, scientists can detect the
DNA associated with HIV (the virus that causes AIDS), Lyme disease, chlamy-
dia, tuberculosis, hepatitis, HPV (human papilloma virus), cystic fibrosis, mus-
cular distrophy, and Huntington’s disease.Gene Therapy: Makes You Feel Better
Gene therapyis a recombinant DNA process, in which cells are taken from the
patient, altered by adding genes, and returned to the patient. A type of genetic
surgery called somatic gene therapymay be possible. Cells of a person with a
genetic disease could be removed, cultured, and transformed with cloned DNA
containing a normal copy of the defective gene. They could be reintroduced into
the individual. If these cells become established, the expression of the normal
genes may be able to cure the patient.
In the early 1990s, gene therapy of this type was used to correct a deficiency
of the enzyme adenosine deaminase(ADA). An immune deficiency disease
patient lacking the enzyme adenosine deaminase, an enzyme that destroys toxic
metabolic byproducts, had been treated. Some of the patient’s lymphocytes were
removed. Lymphocytes are a type of white blood cell that fights infection. The
lymphocytes were given the adenosine deaminase gene with the use of a modi-
fied retrovirus—which served as a vector—and placed back into the patient’s
body. Once established in the body, the cells with altered genes began to make
the enzyme adenosine deaminase (ADA) and alleviated the deficiency.DNA Fingerprinting: Gotcha
DNA fingerprinting is an area of molecular biology that involves analyzing
genetic material. It involves the use of restriction enzymes, which cut DNA mol-
ecules into pieces. When DNA samples obtained from different individuals are
cut with the same restriction enzyme, the number and size of restriction frag-
ments produced may be different. This difference provides the basis for DNA(^134) CHAPTER 8 Recombinant DNA Technology