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Forensic Science - Download as PowerPoint by 2Alffe

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									   DNA STR Typing



          Sherri Phillips
Washington State Patrol Crime Lab
           CODIS Unit
   sherri.phillips@wsp.wa.gov
                   CODIS
Combined DNA Index System

• Used for linking serial crimes and unsolved
  cases with repeat offenders
• Links DNA data in all 50 states
• Searches are conducted routinely to see if there
  are matches between the DNA profile of a
  convicted offender and a crime scene sample or
  between crime scene samples.
        Levels of CODIS
LDIS-Local DNA Index System
 • Tacoma, Marysville, Spokane, Vancouver and
   Seattle-casework
SDIS-State DNA Index System
 • Located in Seattle at Crime Lab Headquarters
NDIS-National DNA Index System
 • Administered by the FBI. Contains the qualifying
   DNA profiles from all fifty states.
 • CO sample must have all 13 loci, Forensic
   Unknowns must have 10 of 13 loci.
               CODIS Hits
Hits in Washington State
• 30 hits in 2008                 2007 CODIS Hits by Crime Type (n=114)


• 114 hits in 2007
• 99 hits in 2006                   homicide 13%

• 90 hits in 2005              other 8%                           burg/theft 33%



• 139 hits in 2004         robbery 14%
                                                                      drugs 0%

• 38 hits in 2003                assault 4%
                                                     sex crimes 28%


• 34 hits in 2002
• 22 hits in 2001
                            --As of 31 January 2008
• Tetra Nucleotide
  repeats
• TPOX – [GAAT]
• Allele
  designation of
  12 mean the
  individual has 12
  [GAAT] repeats
        Format for CO Samples
•   Buccal Swabs on FTA paper
•   Jails, Sheriffs Offices, DOC’s
•   Cotton swab → Foam swab
•   FTA paper-
     Cellulose based paper
     4 chemical substances
     Cells lysed and immobilized
     Stable at room temp for several years
Processing CO DNA samples
                       Extraction            Quantitation
                                               Quantifiler
                         DNA IQ              (Real-Time PCR)
                                                ABI 7000




Data Analysis   Capillary Electrophoresis    Amplification
                                            Identifiler Amp Kit
 GeneMapper          3130xl Genetic           9700 Thermal
  Software             Analyzer                    Cycler
        Extraction (Manual)
• Felon Hit Conformation, Out of Order
  samples and weak samples from Robot
  sets
• DNA IQ kit- silica coated paramagnetic
  resin
• DNA ↑ affinity for silica
• Magnetic stand
                 Quantitation
• Real Time PCR (cycle to cycle change in fluorescents),
  amplifies hTERT locus
• Taq man probe has a 5’ fluorescents reporter dye and a
  3’ non fluorescents quencher
• The probe anneals to sequence between forward and
  reverse primer. When Taq polymerase reaches the
  probe uses the 5’ endonuclease to digest the probe
  releasing the quencher from the fluorescents sequence
• IPC non naturally occurring DNA sequence, detects
  presents of inhibitors
• ABI PRISM 7000 Sequence Detection System
  instrument
                         PCR
• Identifier kit (5 dye)
• FAM (Blue), VIC (Green), NED (yellow), PET (red), LIZ
  (Orange)
• Kit amplifies 15 loci in one reaction
• 30 primers!
• 13 core CODIS loci plus Amelogenin, D2 and D19
• Hot Start PCR (Taq gold) chemically modified at a lysine
  residue, pH dependent
• Below pH 7 modification falls off activating Taq
• Tris Buffer- pH ↓ as temp ↑
• Initial 11 min incubation at 95°C
         Extraction (Robot)
Universal Robot
      Extraction (Robot) cont.
• QIAGEN BioRobot Universal Platform
• Recently validated
• 96 well plate 78 sample
• Fully automated
• Frees up time for data analysis
• Human error rate and chance of contamination
  decreased
• Pipetting is more accurate, faster
• Normalization
Capillary Electrophoresis
 Capillary Electrophoresis cont.
• Automated procedure, minute amount of sample
  used
• 15,000 volts
• high surface area to volume ratio, ↑ heat
  dissipation compared to slab gel.
• POP- Linear uncross-linked dimethyl
  polyacrylamide
• Detection- time span of sample injection to
  sample detection by a laser.
• Internal size standard and allelic ladder
• Electrokinetic injection
           Genemapper ID
•   Software used to analyze CE results
•   Stutter (obts_011708)
•   pull up (mcs_013108, 1 Yellow)
•   tri allele (obts_012208)
•   microvarients (obts_012208)
•   dye blobs
•   spikes
       CODIS vs. Casework
• Decide from a lot of evidence what is the
  most probative
• Screening evidence, time consuming
• Phenol chloroform (organic) extraction,
  time consuming
• Differential extraction
• Mixture interpretation
• Statistic for testifying
       Casework Example
• Angelita Axelson was found strangled
  and raped in a Seattle hotel room on
  June 18, 1981.
• Semen was identified by the medical
  examiner.
• In 2003, detectives in the SPD Cold
  Case unit submitted the evidence to
  the WSP Seattle Crime Lab for STR
  typing.
     Challenges of Decades Old
             Evidence
• Vaginal swabs
  were submitted
  along with other
  evidence.
• Brown swabs -
  usually means
  degraded DNA!
• No DNA profile was
  obtained from
  these swabs.
         Is that all there is?
   (A very important question…..)
• Further
  investigation
  revealed the
  presence of a
  vaginal smear
  prepared at the
  medical examiner’s
  office decades
  ago.
         Testing begins…..
• The cover slip was
  “popped off” the
  vaginal smear and
  the residue was
  scraped into a
  tube.
• The microscopic
  exam revealed the
  presence of
  spermatozoa.

                             SPERM
 A STR/DNA Profile is Obtained
• Upon completion of the DNA testing, nearly a full
  STR profile was obtained from the vaginal smear
  sperm fraction.
• The DNA profile was searched in the convicted
  felon databank.
             A Hit to CODIS!
• The DNA profile from
  the vaginal smear
  sperm fraction
  matches convicted
  felon Bryan Gelenaw-
  aka The Bus Stop
  Rapist.
• When confronted with
  the DNA evidence,         GUILTY!
  Bryan Gelenaw pled
  guilty to the murder of
  Angelita Axelson….

								
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