1. DNA Fingerprinting and Forensic Analysis8
DNA Fingerprinting and Forensic Analysis

2. Introduction to DNA Fingerprinting and Forensics
Chapter Contents
Introduction to DNA Fingerprinting and Forensics
8.1 What Is a DNA Fingerprint?
8.2 Preparing a DNA Fingerprint
8.3 Putting DNA to Use
8.4 DNA and the Rules of Evidence
8.5 Familial Relationships and DNA Profiles
8.6 Nonhuman DNA Analysis
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3. Introduction to DNA Fingerprinting and Forensics
Forensic science – intersection of law and science
Historic examples
1800s – photography
Early 1900s – fingerprints
DNA Fingerprinting – 1985
Unique signature found in each person's genetic makeup
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4. 8.1 What Is a DNA Fingerprint?
Every individual carries a unique set of genes
Chemical structure of DNA is same, but the order of the base pairs differs
Every cell contains a complete set of DNA that identifies the organism as a whole
Only one tenth of 1 percent of DNA differs from person to person
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5. 8.1 What Is a DNA Fingerprint?
Two Main Types of Forensic DNA Testing
RFLP (restriction fragment length polymorphism)
Requires larger amounts of DNA
DNA cannot be degraded
PCR (polymerase chain reaction)
Requires much less DNA
DNA can be partially degraded
Extremely sensitive to contaminating DNA
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6. 8.1 What Is a DNA Fingerprint?
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7. 8.1 What Is a DNA Fingerprint?
DNA profiling depends on a small portion of the genome
variable number tandem repeats (VNTR's)
Repeated sequences of between bp
Each person has some VNTR’s inherited from mother and some from father
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8. 8.1 What Is a DNA Fingerprint?
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9. 8.1 What Is a DNA Fingerprint?
FBI has chosen 13 unique STRs for analysis and comparison in its library of DNA fingerprints
Combined DNA Index System (CODIS)
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10. 8.2 Preparing a DNA Fingerprint
Specimen Collection
Investigators search crime scene for sources of DNA
Working in small groups, make a list of possible sources of DNA that may be found at a crime scene and may be of use in cracking a case
Dirty laundry, licked envelope, cigarette butt, anything else that may be a source for human cells left behind
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11. 8.2 Preparing a DNA Fingerprint
Specimen Collection
Any thing that is a source of DNA can also be a source of contamination!
Collection requires scrupulous attention to detail
Wear disposable gloves; change them frequently
Use disposable instruments
Avoid talking, sneezing, and coughing
Avoid touching any item that might contain DNA (face, nose, or mouth)
Air-dry evidence before packaging; mold can contaminate a sample
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12. 8.2 Preparing a DNA Fingerprint
Enemies of Evidence
Sunlight and high temperature
Bacteria
Moisture
DNA fingerprinting is a comparative process
Samples from crime scene must be compared to suspect DNA
Best sample from suspect DNA is fresh, whole blood
Leukocytes
DNA has been retrieved and analyzed from samples a decade old, using PCR
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13. 8.2 Preparing a DNA Fingerprint
Extraction of DNA
DNA can be purified
Chemically (using detergents)
Mechanically (pressure to force DNA out of cell)
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14. 8.2 Preparing a DNA Fingerprint
PCR – used to amplify DNA found at crime scene into an amount that can be analyzed
DNA primers for the flanking regions of CODIS sites results in DNA amplification at specific STR sites
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15. 8.2 Preparing a DNA Fingerprint
STR Analysis
After STRs are amplified by PCR, alleles are separated and detected using capillary electrophoresis, allowing for the number of repeats in each of the two alleles on a homologous chromosome to be determined
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16. 8.2 Preparing a DNA Fingerprint
STR Analysis, continued
The number of repeats within an STR is referred to as an allele
Ex. The D7S820 STR on chromosome 7 contains between 5 and 16 repeats of GATA
An individual with D7S820 alleles 10 and 15 would have inherited a copy with 10 GATA repeats from one parent and a copy with15 GATA repeats from the other parent
There are 12 different alleles for this STR, and 78 different possible genotypes
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17. 8.2 Preparing a DNA Fingerprint
FBI uses 13 STR regions
Odds that two individuals will have the same 13-loci DNA profile are more than one in a billion
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18. Tests are based on exclusion
8.3 Putting DNA to Use
Evidence collected from a crime scene is compared with evidence collected from a known source
Tests are based on exclusion
Testing continues only until a difference is found
If no difference is found after a statistically acceptable amount of testing, the probability of a match is high
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19. 8.3 Putting DNA to Use
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20. The Narborough Village Murders
8.3 Putting DNA to Use
The Narborough Village Murders
1983 first reported use of genetic fingerprinting in a criminal case
Sexual assault and murder of girl in United Kingdom
The prime suspect's DNA did not match that found at crime scene
Police collected 5500 samples from the area's population of likely suspects
None of the DNA profiles matched the crime scene
Friend of suspect had given a sample in the name of the suspect
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21. 8.3 Putting DNA to Use
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22. DNA first used in United States – 1987
8.3 Putting DNA to Use
DNA first used in United States – 1987
Important use is to refute other erroneous evidence that has sometimes led to false convictions.
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23. Is Eyewitness Testimony More Reliable than DNA Testing?
8.3 Putting DNA to Use
Is Eyewitness Testimony More Reliable than DNA Testing?
Forest Hills Rapist
Victor Lopez tried for the sexual assault of three women
Reported assailant was a black man; Lopez was not a black man
Lopez's DNA was a match to crime scene
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24. Terrorism and Natural Disasters Force Development of New Technologies
8.3 Putting DNA to Use
Terrorism and Natural Disasters Force Development of New Technologies
World Trade Center, September 11, 2001
Used DNA techniques to identify the remains of victims
Tremendous amount of debris, heat, and microbial decomposition of remains
Hundreds of thousands of tissue samples from nearly 3,000 individuals
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25. 8.3 Putting DNA to Use World Trade Center
Evident that new strategies would be necessary to quickly prepare and organize DNA profiles and compare them with DNA profiles from relatives
Within 24 hours, collection points had been established around the city
Family filed missing person reports and provided cheek cell swabs for DNA isolation; personal items from the missing were also collected
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26. 8.3 Putting DNA to Use World Trade Center
Several companies were involved in developing new software programs to help match DNA samples from family members to DNA profiles of victims
Used primarily STR, mtDNA, and SNP analysis
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27. 8.3 Putting DNA to Use South Asian Tsunami December 2004
Lost over 225,000 lives
mtDNA, Y-STR's
Within 3 months, 800 victims had been identified
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28. 8.4 DNA and the Rules of Evidence
DNA fingerprinting had to meet legal standards regarding the admissibility of evidence
5 different standards used
Relevancy test
The Frye standard
The Coppolino standard
The Marx standard
The Daubert standard
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29. 8.4 DNA and the Rules of Evidence
Simpson/Goldman murders
Collected 45 samples for DNA analysis, including known blood samples from the two victims and the suspect; blood drops found at the crime scene, in the suspect's home, and in his car
Pre-trial hearings announced that the DNA collected at the crime scene matched that of O.J. Simpson
Defense lawyers attacked the procedures used in collecting, labeling, and testing the evidence
Possibility that evidence was tainted became obvious
DNA evidence not effective
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30. 8.4 DNA and the Rules of Evidence
Human Error and Sources of Contamination
Chain of custody of samples is compromised
Collection of evidence must be systematically recorded and access to evidence must be controlled
Follow defined standards of laboratory practice and procedures to prevent DNA damage during the analysis
DNA and Juries
Must make sense to the jury
Statistics can be confusing
"1 chance in 50 billion" may lead to focus on the one possibility and discounting the odds against it happening
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31. 8.5 Familial Relationships and DNA Profiles
Paternity Testing
Analyze samples from child and adults involved
Is this man the father of the child?
This test shows that the alleles that do not come from the mother, match this man.
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32. 8.5 Familial Relationships and DNA Profiles
It is possible to draw fetal cells from the amniotic fluid and test for paternity.
This test shows that the alleles that do not come from the mother, match this man.
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33. 8.5 Familial Relationships and DNA Profiles
Mitochondrial DNA
Used to examine samples that cannot be analyzed by RFLP or STR
Older samples that lack nucleated cellular material (hair, bones, and teeth)
Inherited from the mother only
Changes only about 1 percent every million years due to random mutation
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34. 8.5 Familial Relationships and DNA Profiles
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35. 8.5 Familial Relationships and DNA Profiles
Y-Chromosome Analysis
Passed directly from father to son
Useful for tracing relationships among males or analyzing biological evidence involving multiple male contributors
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36. 8.6 Nonhuman DNA Analysis Ginseng
$3 million market in U.S. alone
Two major herbal products are referred to as ginseng
One native to North America, the other native to Asia
Asian ginseng boosts energy; American ginseng calms nerves
American variety is rarer and more valuable
Ancestry of Cabernet Sauvignon Grapes
Hybrid grapes are considered inferior and are legally excluded from bearing the prestigious distinction appellation d’origine contrôlée in France
DNA evidence determined that the ancestors of cabernet sauvignon grapes are cabernet franc and sauvignon blanc
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37. 8.6 Nonhuman DNA Analysis Prove a hunter killed a bear illegally in PA
A law makes it illegal to kill a bear in a den
Witness reported seeing a hunter discharge gun into den
Bear's premolars were removed at registration station to confirm sex and age of bear
Collected blood samples from the den and compared with DNA from bear; were a match
DNA Tagging to Fight Fraud
Use DNA as an authentication label hidden in a wide variety of products
Footballs in 2003 Super Bowl
2000 Sydney Summer Olympics
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