DNA Typing
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DNA strands
come from the
nucleus or the
mitochondria
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DNA Strands
 Building
block of genetic makeup
 A complete copy of an individuals
entire genome exist in nearly
every cell
 Each persons genome is made up
of billions of base pairs
 Most base pairs are “junk” DNA
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DNA is made up
of chromosomes
which contain
matching genes
called alleles
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Base pairs exist at
the basic level of
DNA
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Base Pairs
 Adenine
 Thymine
 Guanine
 Cytosine
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Variable Number Tandem
Repeaters (VNTR)
 Portions
of DNA sequences are repeated
 These repetitions vary among individuals
CACATCTATCTATCTATCTATCTAT
CTATCTATCTATCTATCTATTGC
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Forensic DNA Testing
 Only
one-tenth of a percent of DNA
differs from one human to the next
 This still leaves millions of bases to
analyze for differences
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Types of DNA Testing
PCR
(Polymorphism Chain Reaction)
RFLP
(Restriction Fragment Length
Polymorphism)
STR
(Short Tandem Repeat)
mtDNA
(Mitochondrial DNA Analysis)
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PCR
(Polymorphism Chain Reaction)
 Doesn't
accomplish DNA typing
 Increases the amount of DNA
available for typing by producing
millions of copies
 Use to amplify tiny quantities and
degraded samples
 Extremely sensitive to contamination
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Basic Procedure for
Typing
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DNA is cut into different size
VNTR’s by the use of restriction
enzymes
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Fragments
are placed on
a gel plate
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Fragments are separated by
electrophoresis
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The DNA is then transferred from
the gel plate and made visible
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RFLP
(Restriction Fragment Length Polymorphism)
 Oldest/Cheapest
test
 Requires large amounts of nondegraded DNA
 Utilizes the longer sequences of
VNTR’s
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STR (Short Tandem Repeat) or
SSR (Simple Sequence Repeats)
 Used
to evaluate specific regions
(loci) of DNA strands
 Utilizes shorter stands than VNTR’s
 May by used on much smaller, older,
and more degraded samples
 Usually requires PCR prior to testing
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mtDNA
(Mitochondrial DNA)
 Uses
DNA from a cellular organelle called
a mitochondrion
 Mitochondrial DNA degrades at a much
slower rate than nuclear DNA
 Allows analysis of older biological
samples, such as hair and bones
 Not as precise as STR
 Extremely expensive and time consuming
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Reading DNA Tests
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