Forensic Uses of DNA

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Forensic Uses of DNA

A Conceptual Overview

• 16 March 2011
• Jim Evans MD, Ph.D
• ASTAR Judges Science School
• Chapel Hill, NC

Disclaimer I am not a forensic geneticist
Thanks to Dr. Jennifer Luttman of the FBI (who
is)
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DNA Is In All of Your CellsBody Fluids and
Tissues

• Blood
• Semen
• Saliva
• Perspiration
• Tissue
• Bones and Teeth
• Hair (if there is tissue on the root)
• Urine, Feces, Vomit

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You Leave DNA Everywhere

• Cigarette butts
• Stamps and Envelope flaps
• Drinking cups and Bottles
• Caps
• Gum
• Ear plugs
• Telephone receiver

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Why is DNA Testing Valuable?

• DNA can be retrieved from evidentiary stains and
  tissues
• DNA tests are available
• DNA is unique to you (unless you have an
  identical twin) and therefore very discriminating
• Your DNA is the same, regardless of the body
  fluid or tissue from which it is obtained
• Therefore, DNA obtained from a semen stain from
  an evidentiary item can be compared to that from
  a suspects blood sample
• We can amplify very small amounts of DNA for
  analysis using the Polymerase Chain Reaction (PCR)

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Polymerase Chain Reaction

• Molecular Xeroxing of targeted areas of DNA
  determined to contain information
• Used in
• research
• diagnostics
• forensics

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What DNA tests are used Forensically?

• Former Methods
• Restriction Fragment Length Polymorphism (RFLP)
  Analysis
• PCR-based DQ A1-Polymarker
• Current Method
• Short Tandem Repeat (STR) Analysis by Capillary
  Electrophoresis
• All methods begin with the extraction of DNA
  from the sample and the determination of the
  amount of DNA present in the sample
  (quantitation)

DNA
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Human DNA Testing is Based on Polymorphisms

• Polymorphism many forms
• Our polymorphisms define us as genetically unique
  individuals
• The particular versions of these polymorphisms
  that an indivudal can have are called alleles

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A Human DNA Sequence

• atcgtgactgattaccaggatcctagcggatcctactgacctgacgtacg
  taatgcagtggtcaggttgttcaactcgatgactagaatatatccaggaa
  aatccctgggaaaaattgggccctacgtaccgtaacgttgcaaattcagt
  cggtacgtttccaggctacacacacactgacagatagacagattgtcgtg
  ttatvtgacttggaactgtaggcccttgaatcttggcagtcgtaacgtac
  gtacggtactggtaacgtgaggtcaggttgttcaactcatccaggaaaat
  ccctgggaaaaattgggccctacgtaccgtaacgttgcaaattcagtcgg
  tacgtttccaggctacacacacactgacagatagacagattgtcgtgtta
  tvtgacttggaactgtaggcccttgaatcttggcagtcgtaacgtacgta
  cggtactggtaacgtgaggtcaggttgttcaactcatcgtgactgattac
  caggatctactagaagaaaaattgggccctacgtaccgtaacgttgcaaa
  ttcagtcggtacgtttccaggctacacacacactgacagatagacagatt
  gtcgtgttatvtgacttggaactgtaggcccttgaatcttggcagtcgta
  acgtacgtacggtactggtaacgtgaggtcaggttgttcaactcatccag
  gaaaatccctgggaaaaattgggccctacgtaccgtaacgttgcaaattc
  agtcggtacgtttccaggctacacacacactgacagatagacagattgtc
  gtgttatvtgacttggaactgtaggcccttgaatcttggcagtcgtaacg
  tactagaatatatccaggaaaatccctgggaaaaattggaacgttgcaaa
  ttcagtcggtacgtttccaggctacacacacactgacagatagacagatt
  gtcgtgttatvtgacttggaactgtaggcccttgaatcttggcagtcgta
  acgtacgtagccctacgtaccgtcggtactggtaacgtgaggtcaggttg
  ttcaactcatccaggatt/agatccgtagatcgtaggaaatatctcggat
  aattaacagatacacacccttagaccatttaaatccctgggaaaaattgg
  gccctacgtaccgtaacgttgcaaattcagtcggtacgtttccaggctac
  acacacactgacagatagacagattgtcgtgttatvtgacttggaactgt
  aggcccttgaatcttggcagtcgtaacgtacgtacggtactggtaacgtg
  aggtcaggttgttcaactcatcgtgactgattaccaggatcctagcggat
  cctactgacctgacgtacgtaatgcagtggtcaggttgttcaactcgatg
  actagaatatatccaggaaaatccctgggaaaaattgggccctacgtgtc
  gtaacgtacgtacggtactggtaacgtgaggtcaggttgttcaactcatc
  caggaaaatccctgggaaaaattgggccctacgtaccgtaacgttgcaaa
  ttcagtcggtacgtttccaggctacacacacactgacagatagacagatt
  gtcgtgttatvtgacttggaactgtaggcccttgaatcttggcagtcgta
  acgacgtttccaggctacacacacactgacagatagacagattcaaattc
  agtcccttgaatcttggcagtcgtaacgtacgtacggtactggtaacgtg
  aggtcaggttgttcaactcatcgtgactgattaccaggatcctagcggat
  cctactgacctgacgtacgtaatgcagtggtcaggttgttcaactcgatg
  agaaaaattgggccctacgtaccgtaacgttgcaaattcagtcggtacgt
  ttccaggctacacacacactgacagatagacagattgtcgtgttatvtga
  cttggaactgtaggcccttgaatcttggcagtcgtaacgtacgtacggta
  ctggtaacgtgaggtcaggttgttcaactcatccaggaaaatccctggga
  aaaattgggccctacgtaccgtaacgttgcaaattcagtcggtacgtttc
  caggctacacacacactgacagatagacagattgtcgtgttatvtgactt
  ggaactgtaggcccttgaatcttggcagtcgtaacgtactagaatatatc
  caggaaaatccctgggaaaaattgggccctacgtaccgtaacgttgcaaa
  ttcagtcggtacgtttccaggctacacacacactgacagatagacagatt
  gtcgtgttatvtgacttggaactgtaggcccttgaatcttggcagtcgta
  acgtacgtacggtactggtaa/cgtgaggtcaggttgttcatatatccag
  gaaaatccctgggaaaaattggctacgtaccgtattaactaggatctccg
  atggtacccattaagacacccaaaataggtaacaggtagacatattgata
  cccatagaggatagatttaggacgttgcaaattcagtcggtacgtttcca
  ggctacacacacactgacagatagacagattgtcgtgttatvtgacttgg
  aactgtaggcccttgaatcttggcagtcgtaacgtacgtacggtactggt
  aacgtgaggtcaggttgttcaactcatccaggaaaatccctgggaaaaat
  tgggccctacgtaccgtaacgttgcaaattcagtcggtacgtttccaggc
  tacacacacactgacagatagacagattgtcgtgttatvtgacttggaac
  tgtaggcccttgaatcttggcagtcgtaacgtacgtacggtactggtaac
  gtgaggtcaggttgttcaactcatcgtgactgattaccaggatcctagcg
  gatcctactgacctgacgtacgtaatgcagtggtcaggttgttcaactcg
  atgagaaaaattgggccctacgtaccgtaacgttgtacgtttccaggcta
  cacacacactgacagatagacagattgtcgtgttatvtgacttggaactg
  taggcccttgaatcttggcagtcgtaacgtactagaatatatccaggaaa
  atccctgggaaaaattgggccctacgtaccgtaacgttgcaaattcagtc
  ggtacgtttccaggctacacacacactgacagatagacagattgtcgtgt
  tatvtgacttggaactgtaggcccttgaatcttggcagtcgtaacgtacg
  tacggtactggtaacgtgaggtcaggttgttcaactcatccaggaaaatc
  cctgggaaaaattgggccctacgtaccgtaacgttgcaaattcagtcggt
  acgtttccagctacacacacactgacagatagacagattgtcgtgttatv
  tgacttggaactgtaggcccttgaatcttggcagtcgtaacgtacgtacg
  ggtactggtaacgtgaggtcaggttgttcaactcatcgtgactgattagg
  aaaatccctgggaaaaattgggccctacgtaccgtaacgttgcaaattca
  gtcggtacgtttccaggctacacacacactgacagatagacagattgtcg
  tgttatvtgacttggaactgtaggcccttgaatcttggcagtcgtaacgt
  acgtacggtactggtaacgtgaggtcaggttgttcaactcatccaggaaa
  atccctgggaaaaattgggccctacgtaccgtaacgttgcaaattcagtc
  ggtacgtttccaggctacacacacactgacagatagacagattgtcgtgt
  tatvtgacttggaactgtaggcccttgaatcttggcagtcgtaacgtacg
  tacggtactggtaacgtgaggtcaggttgttcaactcatcgtgactgatt
  accaggatcctagcggatcctactgacctgacgtacgtaatgcagtggtc
  aggttgttcaactcgatgagaaaaattgggccctacgtaccgtaacgttg
  caaattcagtcggtacgtttccaggctacacacacactgacagatagaca
  gattgtcgtgttatvtgacttggaactgtaggcccttgaatcttggcagt
  cgtaacgtacgtacggtactggtaacgtgaggtcaggttgttcaactcat
  ccaggaaaatccctgggaaaaattgggccctacgtaccgtaacgttgcaa
  attcagtcggtacgtttccaggctacacacacactgacagatagacagat
  tgtcgtgttatvtgacttggaactgtaggcccttgaatcttggcagtcgt
  aacgtactagaatatatccaggaaaatccctgggaaaaattgggccctac
  gtaccgtaacgttgcaaattcagtcggtacgtttccaggctacacacaca
  ctgacagatagacagattgtcgtgttatvtgacttggaactgtaggccct
  tgaatcttggcagtcgtaacgtacgtacggtactggtaacgtgaggtcag
  gttgttcaactcatccaggaaaatccctgggaaaaattgggccctacgta
  ccgtaacgttgcaaattcagtcggtacgtttccaggctacacacacactg
  acagatagacagattgtcgtgttatvtgacttggaactgtaggcccttga
  cgtacggtactggtaacgtgaggtcaggttgttcaactcatccaggaaaa
  tccctgggaaaaattgggccctacgtaccgtaacgttgcaaattcagtcg
  gtacgtttccaggctacacacacactgacagatagacagattgtcgtgtt
  atvtgacttggaactgtaggcccttgaatcttggcagtcgtaacgtacgt
  acggtactggtaacgtgaggtcaggttgttcaactcatcgtgactgatta
  ccaggatcctagcggatcctactgacctgacgtacgtaatgcagtggtca
  ggttgttcaactcgatgactagaatatatccaggaaaatccctgggaaaa
  attgggccctacgtgtcgtaacgtacgtacggtactggtaacgtgagg/t
  caggttgttcaactcatccaggaaaatccctgggaaaaattgggccctac
  gtaccgtaacgttgcaaattcagtcggtacgtttccaggctacacacaca
  ctgacagatagacagattgtcgtgttatvtgacttggaactgtaggcgcc
  ttgaatcttggcagtcgtaacgtactagaatatatccaggaaaatccctg
  ggaaaaattgggccctacgtaccgtaacgttgcaaattcagtcggtacgt
  ttccaggctacacacacactgacagatagacagattgtcgtgttatvtga
  cttggaactgtaggcccttgaatcttggcagtcgtaacgtacgtacggta
  ctggtaacgtgaggtcaggttgttcaactcatccaggaaaatccctggga
  aaaattgggccctacgtaccgtaacgttgcaaattcagtcggtacgtttc
  caggctacacacacactgacagatagacagattgtcgtgttatvtgactt
  ggaactgtaggcacacacacactgacagagacagattgtcgtgttatvtg
  acttggaactgtaggcccttgaatcttggcagtcgtaacgtacgtacggt
  actggtaacgtgaggtcaggttgttcaactcatccaggaaaatccctggg
  aaaaattgggccctacgtaccgtaacgttgcaaattcagtcggtacgttt
  ccaggctacacacacactgcagatagacagattgtcgtgttatvtgactt
  ggaactgtaggcccttgaatcttggcagtcgtaacgtacgtacggtactg
  gtaacgtgagagtcaggttgttcaactcatcgtgactgattaccaggatc
  ctagcggatcctactgacctgacgtacgtaatgcagtggtcaggttgttc
  aactcgatgagaaaaattgggccctacgtaccgtaacgttgcaaattcag
  tcggtctagcggatcctactgacctgacgtacgtaatgcagtggtcaggt
  tgttcaactcgatgactagaatatatccaggaaaatccctggactcatcc
  aggaaaatccctgggaaaaattgggccctacgtaccgtaacgttgcaaat
  tcagtcggtacgtttccaggctacacacacactgacagatagacagattg
  tcgtgttatvtgacttggaactgtaggcccttgaatcttggca

• 1/1,000,000th of the Human Genome
• Interspersed with genes
• And polymorphisms which differ between people
• Are sometimes important, influencing traits
• Or medically important characteristics

And serve to make each of us genetically unique
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STRs
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Allele from Mom 3 Repeats (Box cars)
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Evidence Q
DNA Analysis
Compare DNA profiles from the Q to DNA Profile
from the K Does it match???
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Conclusions you can draw from a DNA Match

• Exclusion The DNA profiles being compared do
  not match
• Inclusion You have a DNA match
• Inconclusive - sometimes we do not have enough
  info to make a call (based on the protocol)

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What does a match mean?
The DNAs being tested came from the same source
or
The match is a coincidence
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Coincidence?

• A DNA match is less likely to be a coincidence if
  rare alleles are involved
• Alleles are what geneticists call the different
  versions of a gene out there in the population,
  e.g
• A G vs. a T at a particular polymorphic site
• A 3 STR vs. a 4 STR
• The suspect and the sample from the crime scene
  both have a 3 version of the STR at a
  particular site
• The 3 version is very rare in the population
• Coincidental matches become less likely if
  several different areas of the DNA are tested.
  
• Try to exam 13 locations of the DNA

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Statistical Considerations

• A particular STR may have a 1/10 chance of a
  match
• Two such STRs that match have a chance of
  randomly matching of 1/10 x 1/10 1/100
• Three1/10 x 1/10 x 1/10 1/1,000
• And so on

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How do we know if a genetic type is common or
rare?

• Large numbers of unrelated individuals must be
  tested.
• The frequency of each type must be compiled in a
  DATABASE.
• Frequencies may differ among races, so more than
  one database must be collected.
• FBI routinely uses 4 databases

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Evidence Control and Validation are Critical

• Quality Control/ Quality Assurance
• Training/education
• Validated Procedures
• Protocols (have them and they are being followed)
• Chain of Custody is documented and accurate
• Proficiency tested

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CODIS

• DNA database used to compare samples from crime
  scene to samples from convicted offender
• Link forensic crimes together
• Link unidentified human remains to a missing
  person

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CODIS Architecture
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CODIS Indexes
Unidentified Human Remains
Relatives of Missing Persons
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To consider

• Legislature determining what samples are
  permitted into CODIS
• Which convictions
• Missing persons
• National Standards to ensure the reliability of
  the data
• Audits
• Proficiency Testing
• Training
• Development and validation of new technology
• Gate Keeper

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FBI LABORATORY QUANTICO, VA
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• Its not like TV!!

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• What is Forensic Science?

• Science involving the application of law
• Comparison between an item of evidence and a
  known item

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It all started with the 1983 and 1986 murders of
two schoolgirls in England
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DNA is found in the nucleus of most cell types in
the body
Cell
Nucleus
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Everyone inherits one copy of DNA from their
mother one from their father
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EXAMPLES OF HUMAN POLYMORPHISMS

• Eye color

• Hair color

• Height

• Blood type (ABO, etc.)

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ABI PRISM 310 Genetic Analyzer
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CE Instrument The 310
heat plate
DNA in capillary
sample
detector
-

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STR Profile
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• Cases and Articles

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NO! DNA is used for Identity IssuesDNA
does not prove guilt or innocence
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Masks and Caps

• Items commonly used by bank robbers to disguise
  themselves
• DNA can be obtained from the saliva left on the
  mask or from the sweatband of a baseball cap

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Chewing Gum

• A ring of thieves would steal cars to use as
  their get-a-way vehicles.
• Gum taken from the ignition switch of the stolen
  cars matched one of the suspects
• He confessed and led police to the others involved

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Bandages

• Bank robber covered his face with bandages to
  disguise himself
• He threw them away outside the bank
• DNA recovered from the adhesive portion matched
  the suspect

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September 11, 2001Pentagon
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September 11, 2001World Trade Center
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How do we know DNA is Reliable?
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FBI Directors DNA Standards

• Issued in October of 1998
• Compliance required for participation in NDIS and
  receipt of federal DNA funding
• All forensic DNA laboratories must be accredited
  within 2 years of issuance of the standards

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FBI Directors DNA Standards

• Quality Assurance Program
• Organization and management
• Personnel
• Facilities
• Evidence Control
• Validation
• Analytical Procedures
• Equipment Calibration Maintenance

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FBI Directors DNA Standards

• Reports
• Proficiency testing
• Corrective action
• Audits
• Safety
• Subcontractors

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• Jennifer Luttman

• Forensic DNA Examiner

• 703-632-7517

• 703-632-7620 fax

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Forensic Science Disciplines

• Chemistry
• Fingerprints
• Hairs and Fibers
• Firearms
• Explosives and Devices
• Computer examinations
• Serology
• DNA Analysis- 2 types

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Serology

• Identification of blood and semen through the use
  of presumptive tests and confirmatory tests
• Includes other non-routine procedures (i.e., to
  identify urine, feces, saliva)

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Serology starts with suspect/victims clothing,
weapons, and other evidentiary items