DNa, GeNes, aND BioteChNoloGy 419hoW Do scieNtists apply biotechNology to
issues of coNcerN to humaNs?- Biotechnology is used in experimental gene therapy and
DNA profiling.
taKe-home messaGeDNA analysis has suggested that Thomas Jefferson,
third president of the United States, fathered one or
more children by his slave Sally Hemings. A Fall 2007
article in the University of Virginia Magazine looks
at both sides of this controversial issue. Check out
“Anatomy of a Mystery” at http://uvamagazine.org
/archive. Are you convinced by the arguments on
either side of the issue?thiNk outsiDe the book
vectors used are not effective
enough at delivering the new
genes to cells that need them.
More recently, patients
with a congenital genetic dis-
order that causes blindness
underwent gene therapy that
restored limited vision. To
date, however, gene therapy has been most successful
not for “curing” genetic disorders but for treating cancer.
Trials have targeted malignant melanoma, leukemia, a
fast-growing form of lung cancer, and cancers of the brain,
ovaries, and other organs. In some approaches, tumor cells
are first removed from a patient and grown in the labora-
tory. Genes for an interleukin (which helps activate T cells
of the immune system) are then introduced into the cells,
and the cells are returned to the body. In theory, interleu-
kins produced by the tumor cells may act as “suicide tags”
that stimulate T cells to recognize cancerous cells and
attack them.
At present, gene therapy is still experimental, expen-
sive, and available to only a few carefully selected patients.
It will probably be years before it is widely used for treat-
ing disease.
Genetic analysis also is used
to read Dna fingerprints
Other than identical twins, no two people have exactly the
same sequence of bases in their DNA. Thus each of us has
a DNA profile—a unique set of certain DNA fragments.
When used in the context of a criminal investigation, DNA
profiling produces a DNA fingerprint. DNA fingerprints
are so accurate that they can easily distinguish between
tissues from full siblings.
More than 99 percent of human DNA is exactly the
same in all people, regardless of race and gender. Thus
DNA fingerprinting focuses only on the part that tends to
differ from one person to the next. Throughout the human
genome are short regions of repeated DNA that are very
different from person to person. Each person has a unique
combination of repeats.
Forensic scientists use DNA fingerprinting to identify
criminals and crime victims from the DNA in blood,
semen, or bits of tissue left at a crime scene. Figure 21.21
shows DNA fingerprints that were analyzed in an effort to
identify the perpetrator of a rape. DNA fingerprinting was
a key tool in identifying remains of people killed at the
World Trade Center on September 11, 2001.
Figure 21.20 Gene therapy
helped Rhys Evans, born with
SCID-X1. His immune system
did not develop properly, so his
body couldn’t fight infections.
A gene transfer restored his
immune system. Rhys is now
a healthy, active teenager.
(© Jeans for Gene Appeal)Figure 21.21 Animated! These DNA fingerprints
compare DNA gathered during the investigation of a
sexual assault. The assay compared DNA from the victim
and from the semen of two suspects and the victim’s
boyfriend. Can you see how only one exactly matches
the pattern from the crime scene? Three control samples
were included to confirm that the test procedure was
working correctly.Size ReferenceControl DNASize ReferenceVictimSuspect 1Suspect 2Female CellsSemenSize ReferenceBoyfriendControl DNAControl DNASize ReferenceEvidence from
Crime Scene
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