DNA STR Typing

1
DNA STR Typing

• Sherri Phillips
• Washington State Patrol Crime Lab
• CODIS Unit
• sherri.phillips_at_wsp.wa.gov

2
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.

3
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.

4
CODIS Hits

• Hits in Washington State
• 30 hits in 2008
• 114 hits in 2007
• 99 hits in 2006
• 90 hits in 2005
• 139 hits in 2004
• 38 hits in 2003
• 34 hits in 2002
• 22 hits in 2001
• --As of
  31 January 2008

5

• Tetra Nucleotide repeats
• TPOX GAAT
• Allele designation of 12 mean the individual has
  12 GAAT repeats

6
Format for CO Samples

• Buccal Swabs on FTA paper
• Jails, Sheriffs Offices, DOCs
• Cotton swab ? Foam swab
• FTA paper-
• Cellulose based paper
• 4 chemical substances
• Cells lysed and immobilized
• Stable at room temp for several years

7
(No Transcript)
8
Processing CO DNA samples
9
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

10
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

11
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 95C

12
Extraction (Robot)

• Universal Robot

13
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

14
Capillary Electrophoresis
15
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

16
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

17
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

18
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.

19
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.

20
Is that all there is?(A very important
question..)

• Further investigation revealed the presence of a
  vaginal smear prepared at the medical examiners
  office decades ago.

21
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
22
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.

23
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, Bryan
  Gelenaw pled guilty to the murder of Angelita
  Axelson.

GUILTY!