Demystifying DNA – Demystifying DNA – What is it? How do I get it? What is it? How do I get it? How do I get rid of it? How do I get rid of it? Alissa Bjerkhoel Litigation Coordinator, California Innocence Project Panel Attorney, Appellate Defenders, Inc. Panel Attorney, Sixth District Appellate Program
NOT A SCIENTIST SCIENTIST Disclaimer I AM NOT A SCIENTIST
PRE‐DNA Forensic “Sciences”
Microscopic Hair Comparison
Bullet Comparison
Fingerprint Comparison
Tool Mark Comparison
Tire Tread Impression
Bite Mark Comparison
Shoe Print Evidence
2009 NAS Report “With the exception of nuclear DNA analysis, however, no forensic method has been rigorously shown to have the capacity to consistently, and with a high degree of certainty, demonstrate a connection between evidence and a specific individual or source. “
DNA TESTING
Common Sources *Red blood cells do not contain DNA.
Not So Common Sources Trees and Plants Pets Bugs and Bacteria
Chromosomes 23 pairs of chromosomes 46 total chromosomes
Surrounded by Protein Dense Packets of DNA
Molecular Structure NUCLEOTIDES 1. Base (A, C, G, T). • cytosine (C) • thymine (T) • adenine (A) • guanine (G) 2. Five‐carbon sugar (D). • deoxyribose 3. Phosphate group (P).
Locus The position or location of a particular piece of DNA is commonly referred to as a locus ( loci for more than one). Locus
Genetic Markers Scientists examine the genetic locations (loci) where the number of sequence repeats are the most variable amongst humans
Alleles Each locus (location of DNA on specific set of chromosomes) has two “alleles” Alleles may be dominant or recessive
Genetic Discrimination Variable loci provide the capability of using DNA testing for human identity.
• FLORIDA = 19,550,000 • TAMPA = 352,957 • MAIN STREET = 54 • HOUSE LOCATED AT 123 = 6 • LAST NAME ‐ SMITH = 4 • FIRST NAME ‐ JOHN = 1
PRE‐DNA TYPING Two Main Steps: 1. Extraction 2. Quantification
Isolation/Extraction of DNA
Extraction Techniques Chemical and biological procedures are used to separate DNA molecules from other material .
Quantification
Must quantify the amount of human DNA. Need appropriate DNA levels for subsequent DNA amplification & typing. Optimal amounts result in higher quality data and easier data interpretation
Spectrofluorometers DNA stained with a fluorescent dye. The fluorescent intensity is measured with a spectrofluorometer.
DNA TYPING (profiling/fingerprinting)
RFLP (Restriction Fragment Length Polymorphism)
Alec Jeffreys ‐ 1985
Jul 16, 2010 RFLP , Restriction Fragment Length Polymorphism Flash Lecture,DNA Fingerprinting https://www.youtube.com/watch?v=CfZkn7D6dro
Analysis The size of the target DNA fragments are measured & compared (each fragment length is considered an allele).
Colin Pitchfork
• What they mostly look like:
Other problems with RFLP =
PCR‐Based Testing Methods
https://www.youtube.com/watch?v=2KoLnIwoZKU
PCR Inhibition PCR amplification can be affected by substances known as “inhibitors.”
Early Testing Kits
DQa1 Kits First PCR‐based DNA test kit. Relatively low power of discrimination.
PM‐DQa1 kits (PolyMarker)
PM‐DQa1 kits (PolyMarker)
Short Tandem Repeat (STR)
What is an “STR”? Short segments of our DNA that are next to each other (tandem) and repeat over and over again.
Benefits of More Markers • Over time, DNA breaks down (degrades) • Larger fragments of DNA break down first, smaller later (harder to rip a small piece of paper than a large one)
Post‐Amplification Testing
Amplified product is then subjected to capillary electrophoresis for separation. Alleles are separated by size using a gel or capillary method. The machine produces an electropherogram report.
In two‐minute form . . .
Comparing Reports
YSTR
Y‐STR Detects alleles at different areas on the male chromosome.
Y‐STR Good for cases where lots of female DNA. Passed down from father to son
mtDNA (mitochondrial testing)
About mtDNA is the DNA located inside the mitochondria within cells. mtDNA is organized as a circular, covalently closed, double‐stranded DNA.
mtDNA is inherited solely from the mother.
Nucleotide Position Cambridge Reference Sequence (CRS) Differing Sequences from CRS
Pros Ability to obtain DNA profiles from evidence that is not suitable for nuclear DNA analysis. Helpful in associating maternally related individuals. Lowest power of discrimination. Any maternally related individuals will share the same mtDNA profile. Longest processing time of any DNA test.
How to Get DNA Testing: PENAL CODE SECTION 1405
1405 Requirements (1) CONDITION: Evidence is available and in a condition that would permit DNA testing. (2) CHAIN OF CUSTODY: Evidence to be tested has been subject to a chain of custody. (3) IDENTITY AN ISSUE: Identity of the perpetrator of the crime was, or should have been, a significant issue in the case. (4) MATERIAL: Evidence sought to be tested is material to the issue of the convicted person’s identity as the perpetrator. (5) REASONABLE PROBABILITY: Results would raise a reasonable probability that, in light of all the evidence, the convicted person’s verdict or sentence would have been more favorable. (6) PRIOR TESTING: Evidence was not tested previously or was tested previously, but the requested DNA test would provide results that are reasonably more discriminating and probative of the identity of the perpetrator or accomplice or have a reasonable probability of contradicting prior test results. (7) METHOD: Testing requested employs a method generally accepted within the relevant scientific community. (8) DELAY: Motion is not made solely for the purpose of delay.
Uriah Courtney
TESTING AT TRIAL (2005) – San Diego Sheriff’s Department • Amylase was detected in the crotch of the underwear • DNA analysis performed • Debris observed on toothpicks • DNA analysis performed
THE CONVICTION
CONCESSION & JOINT STIPULATION
POST‐CONVICTION DNA TESTING CALIFORNIA INNOCENCE PROJECT
RESULTS Fingernail scrapings ‐ Victim Vaginal swabs ‐ Victim Underwear – 1 allele
STR RESULTS FROM THE SHIRT
ISOLATING THE PERPETRATOR PROFILE
CALIFORNIA INNOCENCE PROJECT
THE HIT
16 years later
Ronald Cotton – Served 10 years
Richard Jones – Served 17 years
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