Crime Scene Investigation

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Crime Scene Investigation

• DNA fingerprinting
• A technique that generates pattern of DNA
  fragments
• Polymerase Chain Reaction
• Every person has a unique DNA fingerprint (except
  for identical twins)

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DNA Fingerprinting

• PCR allows a very tiny DNA sample to be
  amplified.
• Some uses DNA from one drop of Blood or one hair
  follicle can be isolated amplified using PCR
• Crimes from years ago can be reopened thanks to
  this technique.

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Variable DNA Sequences
The Human Genome 30,000 genes 3 billion bases
We are 99.9 the same
account for the 0.01 differences between
individuals of the human species (300,000 bases)
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DNA Fingerprinting

• PCR
• Polymerase
• Chain
• Reaction
• Agarose Gel Electrophoresis
• Separating and visualizing DNA fingerprints

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PCR is based upon DNA Replication
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PCR technique

• Materials in Test Tube
• DNA to amplify
• DNA Nucleotides (ATCG)
• Primers
• Taq Polymerase from
• Thermus aquaticus.
• A bacteria that resides
• in Hot springs

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PCR technique

• Process involves alternatives cycles of heating
  cooling this mixture.
• Melt Melting DNA double helix
• Anneal primers
• Copy Taq polymerase copies the DNA
• Melt DNA again for another cycle of DNA
  replication

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Short Tandem Repeats (STRs)

• Short tandem Repeats are short sequences of DNA
  that are repeated numerous times in the human
  genome
• The 16 bp sequence GATAGATAGATAGATA is 4 copies
  of the GATA STR.
• The chromosomal locations of STRs are the same
  for every person
• The number of repeats at any given site are
  highly variable for every person.
• PCR can detect these STRs.

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Person A
16 bases
36 bases
5-GENE1GATAGATAGATAGATA GENE2 GATAGATAGATAGATAGAT
AGATAGATAGATAGATA GENE3-3
Person B
24 bases
16 bases
5-GENE1GATAGATAGATAGATA GENE2 GATAGATAGATAGATAGAT
AGATAGENE3-3
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Agarose Gel Electrophoresis

• A technique for separating DNA fragments
• DNA samples amplified by PCR are loaded onto a
  gel
• An electric current is applied to the gel
• DNA fragments separate according to size

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