Forensics

1
Forensics

• Chapter 8

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Central Points

• DNA testing can determine identity
• DNA profiles are constructed in specialized
  laboratories
• DNA profiles used in courts
• Ancestry can be determined by testing DNA
• May refuse to give sample to the police

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8.1 How Is DNA Tested?

• In 1975, in England
• Dr. Alec Jeffreys developed DNA fingerprinting to
  compare DNA profiles from different individuals
• Used to solve murders (see Narborough Village
  Murders)

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Spotlight on Law Narborough Village

• In 1989, first case that used DNA profile for
  evidence
• Rape and murder of two girls in a small English
  village within 3-year period
• Buckland confessed to one murder
• DNA analysis, one man killed both but not
  Buckland
• DNA dragnet of gt 4,000 men, no match
• Colin Pitchfork paid someone to give sample but
  caught because of overheard conversation

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8.2 DNA Profile (DNA Fingerprint)

• Variations in
• Minisatellites (repeated sequences, 10100 base
  pairs)
• Short tandem repeats (STRs) (29 base pairs)
• Single nucleotide polymorphisms (SNPs)
• DNA variations can be used to create DNA profile
  and ID individuals
• Used in criminal cases, paternity lawsuits, and
  studies of human evolution

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Variations in DNA

• Minisatellites
• Short tandem repeats (STRs)
• Single nucleotide polymorphisms (SNPs)

...CCTGACTTAGGATTGCCA...
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Methods to Prepare DNA Profiles

• Two common methods
• Restriction fragment length polymorphism (RFLP)
  analysis
• Polymerase chain reaction (PCR)

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RFLP Analysis

• Large amount of blood or tissue
• Steps
• DNA extracted
• Cut into fragments using restriction enzymes
• Fragments loaded on agarose gel
• Electrical current passed through gel, DNA
  fragments migrate and separating by size
• Pattern fragments photographed and compared to
  others

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Steps in RFLP
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RFLP
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PCR

• Small amount of DNA sample
• Steps in one cycle
• DNA placed in solution
• Heated, double-stranded DNA separates
• Temperature lowered, primers mixed with DNA
• Primers pair with complementary regions on DNA
• DNA polymerase uses nucleotides to synthesize
  double-stranded DNA molecule

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Steps in PCR
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Using PCR to Increase DNA
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Animation

• http//www.dnalc.org/resources/3d/19-polymerase-ch
  ain-reaction.html

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STR Allele, a Unique Number of Repeats

• 29 nucleotides long
• Example of three alleles
• Allele 1 AGA
• Allele 2 AGAAGAAGA
• Allele 3 AGAAGAAGAAGAAGA
• Analysis of several STR alleles show frequency of
  specific combinations

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PCR for DNA Profile

• Steps
• DNA sample analyzed for STR alleles present in
  population members
• Analyze population frequency, how often
  combinations of alleles present
• Population frequencies for each STR allele
  multiplied to estimate probability

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Combined Frequencies
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DNA Samples (1)
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DNA Samples (2)
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Animation Studying and Manipulating Genomes (DNA
fingerprinting)
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Animation Whodunnit? A DNA fingerprint crime
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8.3 DNA Profiling and U.S. Courts

• Landmark case Frye v. U.S.
• DNA entered U.S. court system in 1989
• Approved for use in courts all over the country
• Evidence may be challenged

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How Are DNA Profiles Used?

• Material from crime scene analyzed, compared to
  other samples or data base
• Combined DNA Index System (CODIS) panel of 13
  STRs for DNA profiles
• 30 of DNA profile results clear innocent people

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DNA Profile Comparison
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DNA Databases

• Since 1998, FBI enters DNA profile from felons
• More than 1,700,000 profiles
• DNA databases becoming important tools in solving
  crimes

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8.4 Other Uses for DNA Profiles

• Czar Nicholas II and family
• Remains of military personnel killed in action
• Victims of 9/11 and Katrina
• Paternity identification
• Trace our ancestry

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Czar Nicholas II
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Tracing Ancestry

• Mitochondrial DNA testing
• Mitochondria organelle with DNA
• Maternal inheritance, passed from mother to
  children
• Use haplotypes to trace maternal ancestry
• Y chromosome testing
• Y chromosome passed father to son
• Use haplotypes to trace paternal inheritance

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Mitochondrial Inheritance
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Y Chromosome Inheritance