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Forensics. Chapter 8. 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. 8.1 How Is DNA Tested?. In 1975, in England - PowerPoint PPT Presentation
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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
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)
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 > 4,000 men, no match Colin Pitchfork paid someone to give sample but
caught because of overheard conversation
8.2 DNA Profile (DNA Fingerprint)
Variations in:• Minisatellites (repeated sequences, 10–100 base
pairs)• Short tandem repeats (STRs) (2–9 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
Minisatellites
Short tandem repeats (STRs)
Single nucleotide polymorphisms (SNPs)
Variations in DNA
...CCTGACTTAGGATTGCCA...
Methods to Prepare DNA Profiles
Two common methods:
Restriction fragment length polymorphism (RFLP) analysis
Polymerase chain reaction (PCR)
RFLP Analysis
Large amount of blood or tissue
Steps:
1.DNA extracted
2.Cut into fragments using restriction enzymes
3.Fragments loaded on agarose gel
4.Electrical current passed through gel, DNA fragments migrate and separating by size
5.Pattern fragments photographed and compared to others
PCR
Small amount of DNA sample
Steps in one cycle:
1.DNA placed in solution
2.Heated, double-stranded DNA separates
3.Temperature lowered, primers mixed with DNA
4.Primers pair with complementary regions on DNA
5.DNA polymerase uses nucleotides to synthesize double-stranded DNA molecule
STR: Allele, a Unique Number of Repeats
2–9 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
PCR for DNA Profile
Steps:
1.DNA sample analyzed for STR alleles present in population members
2.Analyze population frequency, how often combinations of alleles present
3.Population frequencies for each STR allele multiplied to estimate probability
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
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
DNA Databases
Since 1998, FBI enters DNA profile from felons
More than 1,700,000 profiles
DNA databases becoming important tools in solving crimes
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
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