The ABCs & 123s of DNA Testing

Transcription

1 The ABCs & 123s of DNA Testing By Jenny S Cheung & Allison Lewis Legal Aid Society DNA Unit Training for Federal Defenders October 7,

2 TOPICS What is DNA How do they test DNA Discovery in a DNA case What to do with DNA evidence 2

3 What is DNA Genetic blueprint for all life Found in nucleated cells (eg not red blood cells = no nucleus) 23 pairs of chromosomes in each cell - full copy of War & Peace Same copy in every cell (skin, blood, semen, etc), trillions of cells in the body 3

4 high school bio 4

5 The double helix coded information A + T G + C the code is a sequence of A/T and G/C, repeating in a pattern like language or music 5

6 nucleotides Guanine always goes with Cytosine Adenine always goes with Thymine 6

7 but most of our DNA is 99% shared DNA e.g., basic eye DNA rods & cones retina pupil small portion unique the same eye color, specks, tendency to vision problems AND our junk DNA 7

8 Forensic DNA evolutionary relic ( tail DNA ) junk DNA doesn t code for anything anymore blah blah blah DNA (v. Beethoven score) 8

9 TOPICS What is DNA How do they test DNA Discovery in a DNA case What to do with DNA evidence 9

10 short repeats repeat (STRs) short tandem repeats e.g.: [AATC] or [TACG] repeat 4 allele = [AATC] [AATC] [AATC] [AATC] 6 allele = [AATC] [AATC] [AATC] [AATC] [AATC] [AATC] at that page (location) the person is a 4, 6 at each location, there are a number of possible alleles or numbers of repeats 10

11 Target Junk DNA certain pages are ripped out and copied 11

12 LOCI (plural of locus, or location) was 13, now 16, soon 24 currently, OCME examines the STRs at 16 locations moving to 24 loci in 2017 some are labelled by coordinates (D8S1179 = DNA chromosome 8, Site 1179); some have random names (TPOX, THO1, vwa) 12

13 high school bio D3S1358 D8S

14 DNA Profile TPOX D3S1358 FGA D8S1179 D21S11 VWA Count how many times the STRs repeated at the loci. The # of repeats is called the alleles. The DNA profile is just a chart of the alleles at the 16 loci TPOX D3S1358 FGA D8S1179 D21S11 D7S820 CSF1PO THO1 D13S317 D16S539 D2S1338 D19S433 D18S51 D5S818 vwa AMEL 10,14 5, 14 7,10 12, , ,13 23, ,17 10,13 5,14 XY 14

15 each location is one section of the electropherogram heterozygote homozygote 15

16 Random Match Probability ( RMP ) RMP = chance that a randomly selected unrelated person will have same profile at each loci Used only for single source DNA Enough uniqueness at enough locations to get a staggering statistics (1 in 6.8 trillion) The product rule: 10% of the population is a 4, 2% is a 5 at a certain location (allele frequency) 10% (.10) x 2% (.02) =.2% (.002) 16

17 The statistical myth of 1,000 planet earths Based on a small pool of allelic frequency data, the RMP is calculated to 1 in 6.80 trillion (a bottom estimate), so criminalists will testify you need to have 1,000 planet earths to see that profile again. Statistically true; not actually true and very misleading. 17

18 Mixture of DNA single source = max 2 alleles (mom and dad) at each locus if 3 or more, must be at least 2 people if 5 or more, must be at least 3 people 18

19 Deconvolute, or deduce, the Major Contributor ~ like voices, louder versus softer ~ 19

20 Likelihood Ratio was used when you cannot identify the major contributor in a mixed profile soup of alleles LR = a ratio likelihood of prosecutors theory (your client in the mixture) = THE NUMERATOR vs. likelihood of defense theory (your client not in the mixture) = THE DENOMINATOR 20

21 Forensic Statistical Tool ( FST ) OCME created likelihood ratio program First, evidence defined as a mixture then with comparison sample, determine whether excluded if not, FST calculation ran It is 1.2 million times more likely if the victim and the suspect are the contributors to this 2 person mixture rather than the victim and unknown person They can also insert a known contributor (rape CW, known sex partner, homeowner, etc.) Frye challenge won - P v. Peaks and Collins, 49 Misc.3d 595 (Kings County, Dwyer, J. 2015) Daubert challenges continue US v. Johnson, No. 1:15-cr VEC (SDNY, July 6, 2016 (Caproni. J) 21

22 OCME changes!! OCME announced changes effective 1/1/17 no more RMP - but all LR no more FST - but STRmix 22

23 23

24 Steps of DNA Testing Extraction Quantitation Amplification Electrophoresis Analysis & Interpretation 1. GET A DNA SAMPLE TO BE TESTED 2. EXTRACTION: Set the DNA free from the cell 3. QUANTITATION: How much DNA is there? 4. AMPLIFICATION: Make millions of copies of the targeted STRs 5. ELECTROPHORESIS: Separate amplified DNA fragments by size 6. ANALYSIS & INTERPRETATION: Quantitatively and qualitatively compare the DNA evidence sample to a known DNA profiles Polymerase Chain Reaction (PCR) to target and duplicate the STRs at the loci (locations) that we want to measure 24

25 Quantitation It s about the CONCENTRATION of DNA per microlitre Ideal amount for testing to get results but not overblown machine - Goldilocks principle OCME will micro-con (add or take away H₂0) 25

26 DNA Measurements picogram - 1,000,000th of a grain of sugar microlitre - 1,000,000th of a liter of soda one human cell contains ~ 6 pg of DNA one fingerprint has ~ 100 pg of DNA 26

27 TOPICS What is DNA How do they test DNA Discovery in a DNA case What to do with DNA evidence 27

28 Discovery Lab Report Forensic Biology (FB) files Electronic Raw Data 28

29 FB file FB (Forensic Biology) File Rule of Thumb - if you can staple it, you haven t received the full FB file TWO PARTS: evidence file (FB ) suspect file (FBS ) Motion to Compel (depends on ADA) Or subpoena if ADA didn t get it (or Brady?) 29

30 What does each OCME FB files contain? Evidentiary FB File Intake of the evidence Examination of stains (serology) Processing of exemplars (i.e., CW) for elimination Bench notes for each step of the DNA testing Suspect FB File Intake of the evidence (e.g., buccal swab, cig butt) Bench notes for each step of the DNA testing Communications between OCME & law enforcement DNA databank searches [FB ] [FBS ] Report in this file is OCME S conclusions about the evidence only 30 Report in this file is OCME s conclusions of the comparison of the suspect s profile to the evidence

31 Two sides to every FB file Left side of the FB File : Police reports Vouchers Correspondences btw OCME & law enforcement Database searches Schedule of Analysis Right Side of the FB File : Intake of the Evidence Serology testing (if evidentiary file) All the steps of DNA testing Chronology is bottom up 31

32 Serology Testing (Evidentiary File) For stains in the evidence, OCME will use either presumptive or confirmatory tests to assess what the biological fluid is o o Presumptive tests: Can t say definitely Confirmatory tests: More definitive SEROLOGY PRESUMPTIVE CONFIRMATORY BLOOD Kastle Meyer (KM) Takayama or HemaTrace AMALYSE Alpha amalyse or RSID Saliva None SEMEN AP / PSA or P30 Christmas tree stain 32

33 Electronic Raw Data (ERD) - Electronic files (.fsa form) - Data before processed by GeneMapper or any software - Unfiltered, none of OCME parameters or filters yet - Allows your expert to run it and see data not included in OCME file - DISCOVERY v SUBPOENA - NOTE - OCME no longer takes a position regarding subpoena 33

34 TOPICS What is DNA How do they test DNA Discovery in a DNA case What to do with DNA evidence 34

35 Get to know your local lab call to meet with your criminalist; OCME reporting analyst is listed at the end of the reports go prepared; they are known to report back to the ADA read (or get) their protocols on their website, technical manuals 35

36 Essential DNA Principle Locard s principle of exchange perpetrator of a crime will bring something to it and take away something from it Direct Transfer Secondary Transfer - via intermediary Tertiary Transfer - via two intermediaries 36

37 the studies many studies out there varying results read the OCME studies if you have a study you like, try to get the criminalist to read it before trial - strategize Could Secondary DNA Transfer Falsely Place Someone at the Scene of a Crime? U. of Indianapolis (Cynthia Cale, et. al, 2015) 37

38 not guilty Case of CA v Lukis Anderson 38

39 OCME cannot tell us When was DNA deposited on item? long before crime and separately (innocent explanation) after crime (contamination) How was DNA deposited? directly from client via intermediary How long has DNA been on the item? People v Persons 74 AD.3d 1239 (2d Dept 2010) 39

40 Flawed Gov t Arguments Your client is the major contributor to the mixture, and therefore he touched the item last - NOT TRUE! he touched the item more than others - NOT TRUE! he left the item at the scene - NOT TRUE! Incriminating LR statistics means your client is in the mixture - NOT TRUE! People v. Ramsaran, 35 NYS3d 549 (2016) Mixture found on defendant s shirt. CW is a possible contributor. Gov t inappropriately argued that CW s DNA was on the shirt. Conviction reversed. Gov t cannot overstate the significance of the DNA evidence People v. Wright (COA) NY Slip Op D could not be excluded from a pool of possible contributors. Gov t argued that D left his DNA all over the crime scene. Conviction reversed. 40

41 DNA for the Defense Theory!! Challenge the science or stats Adopt the DNA and embrace What didn t they test? DNA inconsistent with their version Transference? Contamination? 41

42 Thank you!! DNA UNIT, LEGAL AID SOCIETY David Loftis (AIC): Daniel Ades (Central/SI): Jenny Cheung (Queens): Julie Fry (Central/SI): Celia Givens, (Paralegal): Jessica Goldthwaite (Bronx): Shilpy Goswami (on leave) Clinton Hughes (Brooklyn): Allison Lewis (Manhattan): Richard Torres (Central):