Introduction To DNA Testing Innocence Network Conference 2012

1. Introduction To DNA TestingInnocence Network Conference2012 Olga Akselrod Staff Attorney The Innocence Project

2. DNA Basics – What Is DNA? • Deoxyribonucleic acid (DNA) is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms • Two kinds of DNA: • Nuclear • Mitochondrial

3. DNA Basics – What Is DNA? • Nucleas = 46 Chromosomes • 23 from egg (mother) • 23 from sperm (father) • Many Mitochondria

4. Target Region for PCR Nuclear DNA Testing What genes are we looking at? Base Pair mutations in highly variable regions in the DNA Base pairs: adenine (A) forms a base pair with thymine (T) and guanine (G) forms a base pair with cytosine (C) We test these regions because they vary greatly from person to person, not because they have a specific genetic purpose Image: greghampikian@boisestate.edu

5. To Get A DNA Profile, Just Count The Number of Repeats DNA testing kits test at 13-16 regions (aka “markers” or “loci”) At each locus, you have genetic information inherited from your mom and your dad in the form of a number of repeats. The number of repeats are called “alleles”. Image: greghampikian@boisestate.edu

6. Nuclear DNA Testing - Statistics The probability of a random match is calculated by applying the product rule to the probability of the allele found at each locus 0.195 x 0.075 = 0.0146 = 1 in 68 people (1/.0146) 0.195 x 0.075 x 0.036 = 0.0005 = 1 in 2000 people (1/.0005) Etc. Multiply them ALL together and you get 1 in 594 trillion! Modified from DNA.gov

7. Old DNA Testing Methods • RFLP: late 1980s-early 1990s • Very discriminating • Not very sensitive • DQ Alpha: early 1990s-mid/late 1990s • More sensitive than RFLP, but less discriminating • More sensitive because was first method to use PCR • Same basic principle as current testing but different markers • DQ Alpha Polymarker – Additional polymarker enzymes added to make the test more discriminating

8. Current DNA Testing Methods • STR (Short Tandem Repeat): late 1990s-present • Advantages • Much more sensitive than older methods • Number of markers makes it highly discriminating • Compatible with CODIS • Allows for sex typing • (Differential extraction was also developed around the same time)

9. Current DNA Testing Methods • Y-STR (Y Chromosome DNA Testing): early 2000s-present • Variant of autosomal STR that tests for DNA in the Y chromosome • Advantages • Good for use in samples with little male DNA and lots of female DNA • Good for use in samples with DNA from multiple males • Paternally inherited so you can use relatives’ DNA as elimination samples • Disadvantages • Paternally inherited so it’s not as discriminating as STR • Not compatible with CODIS • Can’t be used where paternal relative or female is alternative suspect

10. Current DNA Testing Methods • MiniFiler STR: late 2000s – present • Advantages • Good for degraded samples • More sensitive so less DNA needed • Good as adjunct to STR • Where STR only gets partial profile, miniSTR may help to obtain a more complete profile • Disadvantages • Because it is more sensitive, can produce complex mixed profiles, including contaminants • Other Newer Kits That May Be Good for Degraded/Inhibited Samples • Powerplex Hot Start (HS) 16 • Identifiler Plus

11. Current DNA Testing Methods • Mitochondrial DNA testing: late 1990s-present • Advantages • Good for testing hairs without roots • Maternally inherited so you can use relatives’ DNA as elimination samples • Disadvantages • Maternally inherited so less discriminating • Not compatible with CODIS or state databases • Mixtures are extremely difficult to interpret

12. Strategies For Using DNA To Exonerate • Three main ways that DNA can be used to prove innocence: • Exclusion of defendant from probative item • Exclusion plus getting redundancy • Exclusion plus identifying contributor of DNA

13. Strategies For Using DNA To Exonerate • Strategy #1 – Exclusion of the defendant from DNA on a probative item • Exclusion may be sufficient if there is evidence that biological material you want to test came from the perpetrator, i.e.: • Intimate samples – semen or foreign pubic hair from rape kit • Cigarette that witness saw perpetrator smoke • Drink or food that witness saw perpetrator drinking or eating

14. Strategies For Using DNA To Exonerate • Strategy #1 – Exclusion of the defendant from DNA on probative item (cont.) • Could someone besides the perpetrator have deposited the biological evidence? • Often exclusion alone isn’t sufficient because there are alternative explanations for the source of the biological material • Blood at crime scene where struggle occurred • Hair on victim or near victim • DNA in fingernail scrapings/clippings • Sweat and skin cells on clothing worn by perpetrator • Even in rape cases where testing semen, you need to exclude the other possibilities, such as consensual sex partners • If it isn’t an intimate sample or the DNA cannot conclusively be attributed to the perpetrator, you will likely need more than just an exclusion

15. Strategies For Using DNA To Exonerate • Strategy #2 - Exclusion plus getting redundancy • If uncertain that biological material from a single item comes from the perpetrator, a redundancy to other biological material connected to crime can build a stronger case • Get the same person’s profile on multiple probative items i.e., perpetrator’s clothing, ligature, and blood on floor; or • Multiple crime scenes exhibit same DNA profile with strong MO • May also be important where defendant was excluded at trial • Prosecution argues DNA not from perpetrator, but redundancy makes that argument less plausible • Note that you can’t compare DNA test results from different methods (i.e. a Mito result can’t be compared with an STR result), so if you need a redundancy to exonerate, must be careful in selecting methods to use.

16. Strategies For Using DNA To Exonerate • Strategy #3 – Excluding plus identifying actual perpetrator • Two ways • CODIS– state and federal DNA databases • Compare DNA from alternative suspect • May also be a good strategy where defendant already excluded pretrial through serology or early DNA but was still convicted • i.e. Doug Warney and Jeff Deskovic

17. Strategies For Using DNA To Exonerate • Even if the DNA test results are unable to prove actual innocence, they may demonstrate a right to a new trial by showing attribution was incorrect, for example: • DNA testing disproves serology inclusion of blood on defendant’s clothes attributed to victim • DNA testing disproves hair microscopy inclusion

18. Post-conviction DNA Testing Is Still A Good Call Even Though . . . • Hair microscopy connects defendant to the crime • Serology included the defendant • How many enzymes? • Lack of results pretrial • What methods did the lab use? • Could they have missed biological material? • Could they have not used enough sample? • Partial DNA match • What is the inclusion statistic? • Did they use an early kit with few markers?

19. Postconviction DNA Testing Is A Good Call When . . . • Some factual scenarios make finding DNA MORE likely • Victim says perpetrator ejaculated or semen/sperm found pretrial; nothing about condom • Earlier results detected foreign antigens/alleles • Nature of the crime • Try to reconstruct the crime from testimony, photos, reports etc. to help determine whether perpetrator would have left behind DNA • Signs of struggle = increased chance that perp was injured • Defensive wounds • Overturned furniture; general disarray • Strangulation makes DNA in fingernail scrapings more likely • Violent stabbing makes finding perpetrator blood more likely • Hot weather or level of struggle can make perpetrator sweat and skin cells more likely on perpetrator clothes left at crime scene • Other logical inferences

20. DNA Testing Won’t Always Make Sense • DNA helps us establish identity, so if identity isn’t at issue, it probably isn’t a DNA case • Consent defense • Self defense • Other fabrication cases • Biological material lacks strong connection to the crime

21. DNA Testing Is Not A Panacea • Biological material is rarely left behind by the perpetrator • Less than 10% of criminal cases • Problems with partial profiles • Problems with interpreting mixtures • Innocent transfer • Doesn’t solve tunnel vision

22. Contact Information Olga Akselrod Staff Attorney The Innocence Project 212-364-5348 oakselrod@innocenceproject.org