Evaluating Evidence

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DNA Fingerprinting

• Evaluating Evidence

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DNA Fingerprinting can be used in paternity
testing or murder cases.
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DNA Fingerprint Basics

• Different individuals carry different alleles.
• Most alleles useful for DNA fingerprinting differ
  on the number of repetitive base sequences they
  contain.
• Restriction enzymes are used to cut the DNA along
  these repetitive sequences.

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DNA Fingerprint Basics

• If DNA is cut with a restriction enzyme that
  recognizes sites on either side of the region
  that varies, DNA fragments of different sizes
  will be produced.
• A DNA fingerprint is made by analyzing the
  different sizes of DNA fragments produced from a
  number of different sites that vary within the
  genome.

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DNA Fingerprint Basics

• DNA fragments of different size will be produced
  by a restriction enzyme that cuts at the points
  shown by the arrows.

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DNA fragments are then separated based on size
using gel electrophoresis.
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Results

• In a standard DNA fingerprint, as many as a dozen
  sites can be analyzed with each site having many
  possible combinations of alleles.
• When many genes are analyzed, each with many
  different alleles the chance that two sites will
  match is 1 in 100 billion when no lab err is
  factored in.

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A DNA fingerprint from a murder case
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A DNA fingerprint from a paternity test
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Unlike a conventional fingerprint that occurs
only on the fingertips and can be altered by
surgery, a DNA fingerprint is the same for every
cell, tissue, and organ of a person. It cannot be
altered by any known treatment. Consequently, DNA
fingerprinting is rapidly becoming the primary
method for identifying and distinguishing among
individual human beings.
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An additional application of DNA fingerprint
technology is the diagnosis of inherited
disorders in adults, children, and unborn babies.
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The technology is so powerful that, for example,
even the blood-stained clothing of Abraham
Lincoln could be analyzed for evidence of a
genetic disorder called Marfan's Syndrome.
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DNA FingerprintingIt was at 9am on Monday
September 15, 1984 when Sir Alec Jeffreys removed
some X-ray film from its developing tank that he
experienced a rare, serendipitous moment in
science.
He had been looking for good genetic markers
for basic genetic analysis, but had accidentally
stumbled upon a way of establishing a human's
genetic identification.
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By that afternoon, he and his colleagues had
named their discovery DNA fingerprinting.
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His technique has subsequently been applied to a
wide range of problems in genetics. These include
developing genetic markers for medical research
and the diagnosis of inherited disorders
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DNA fingerprinting is also used in the solving of
crimes, establishing family relationships - for
example in paternity and immigration disputes,
and also in breeding programs in a number of zoos
and conservation centers to establish family
relationships within captive colonies of
endangered species of animals and birds to
minimize inbreeding and maintain genetic
diversity.
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Fingerprinting a Crime Suspect
There are three basic components to a DNA
fingerprint test. 

• First, there is the DNA from the crime scene
• Second, there is the DNA from a suspect
• Third, there is DNA with known attributes that is
  used as a control. 

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Problems with DNA Testing
Many have questioned the validity of DNA
fingerprinting test results.  Because the burden
of proof is on the forensic scientists, there are
safeguards in place to be sure that DNA
fingerprinting results are accurate.  The first
is the control DNA that runs through the tests
alongside the suspect's DNA and the DNA found at
the crime scene.  If the control DNA tests
properly, then the DNA in question tested
properly as well.  Another safeguard in place is
that the test is run four times using four
different restriction enzymes.  In order to be
absolutely positive of a match, all four sets of
DNA from the crime scene must match all four sets
of DNA from the suspect.  With these safeguards
in place, the odds are one in 70 billion (140
times Earth's population) that the results are
inaccurate.
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Final Review
In conclusion, when one thinks of DNA
fingerprinting and the biological processes
associated with it, it becomes difficult to
identify the chemical steps necessary to perform
such a complex task. Yet, when considered at the
molecular level, the building blocks of DNA and
the fingerprinting process have very much to do
with chemical reactions that take place inside of
each organic particle. Thus, without chemistry,
geneticists would never be able to fully
comprehend the complex workings of even the
tiniest biological forms, such as DNA, which
would never fully take form without the basis of
chemical exploration.
Please pay careful attention to these notes, you
will be tested on them later.
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References

• Rosner, D. 2004. How Does DNA Fringerprinting
  Work? http//www.thenakedscientists.com/HTML/artic
  les/article/dalyacolumn8.htm/ Accessed 2008 Apr
  26.
• Sha, K. 2004. How Does a DNA Paternity Test
  Work? http//www.thetech.org/genetics/ask.php?id2
  0 Accessed 2008 Apr 26.
• Author Unknown http//fig.cox.miami.edu/cmallery/
  150/gene/mol_gen.htm Accessed Apr 26