DNA Fingerprinting
Other than identical twins, no two individuals have the same
genetic material. Scientists use DNA sequencing gel technology to
determine a DNA fragment’s nucleotide sequence, as shown in
Figure 9.Because the places a restriction enzyme can cut depend
on the DNA sequence, the lengths of DNA restriction fragments
will differ between two individuals. Such DNA fragments of differ-
ent lengths (polymorphisms) are called restriction fragment length
polymorphisms, or RFLPs.
RFLPs can be used to identify individuals and to determine how
closely related members of a population are to one another. The
Southern blot technique, shown in Figure 5, is used to show an
individual’s RFLP profile. The result is called a
DNA fingerprint. A is a pattern
of dark bands on photographic film that is
made when an individual’s DNA restriction
fragments are separated by gel electrophoresis,
probed, and then exposed to an X-ray film.
Because restriction enzymes cut the DNA from
different individuals into DNA fragments of dif-
ferent lengths (RFLPs), each individual (other
than identical twins) has a unique pattern of
banding, or DNA fingerprint.
The banding patterns from two individuals
can be compared to establish whether they are
related, such as in a paternity case. Because it
can be performed on a sample of DNA found in
blood, semen, bone, or hair, DNA fingerprinting
is useful in forensics. Forensics is the scientific
investigation of the causes of injury and death
when criminal activity is suspected. DNA finger-
prints are also valuable for identifying the genes
that cause genetic disorders, such as Hunting-
ton’s disease and sickle cell anemia.
DNA fingerprintSECTION 2 Human Applications of Genetic Engineering 237
Section 2 Review
Relatethe use of genetic engineering to
the treatment of human illnesses such
as hemophilia. 3F 6A 6DRelategenetic engineering techniques to the
making of vaccines. 6A 6DNamethe process in which a healthy copy of a
gene is inserted into the cells of a person with
a defective version of the gene. 6A 6DListtwo ways in which DNA fingerprinting has
been useful to society. 3C 6A 8BCritical ThinkingDistinguishing Relevant
Information A student states that genetic engi-
neering is “perfectly safe and sound.” What
safety and ethical issues do you think might arise
over the use of genetic engineering? 3COne medicine made in bacte-
ria using genetic engineering techniques is
insulin, which is used to treat 4D
Aheart attacks Cdiabetes
Bsmallpox Dcystic fibrosisTAKS Test PrepTAKS Test PrepFigure 9 DNA sequence.
The nucleotide sequence of
DNA fragments can be deter-
mined using DNA sequencing
gel technology.