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Chapter 8

Chapter 8. DNA Fingerprinting and Forensic Analysis. Chapter Contents. 8.1 Introduction to DNA Fingerprinting and Forensics 8.2 What Is a DNA Fingerprint? 8.3 Preparing a DNA Fingerprint 8.4 Putting DNA to Use 8.5 DNA and the Rules of Evidence

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Chapter 8

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  1. Chapter 8 DNA Fingerprinting and Forensic Analysis

  2. Chapter Contents • 8.1 Introduction to DNA Fingerprinting and Forensics • 8.2 What Is a DNA Fingerprint? • 8.3 Preparing a DNA Fingerprint • 8.4 Putting DNA to Use • 8.5 DNA and the Rules of Evidence • 8.6 Familial Relationships and DNA Profiles • 8.7 Nonhuman DNA Analysis

  3. 8.1 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

  4. 8.2 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% of DNA differs from person to person

  5. 8.2 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) • Less DNA and DNA can be partially degraded • Extremely sensitive to contaminating DNA

  6. 8.2 What Is a DNA Fingerprint? • DNA profiling depends on a small portion of the genome • Exons code proteins • Introns do not code for proteins • The introns contain repeated sequences of between 1 and 100 base pairs • Called variable number tandem repeats (VNTR’s) • Some VNTR’s are inherited from mother and some from father

  7. 8.2 What Is a DNA Fingerprint?

  8. 8.2 What Is a DNA Fingerprint? • DNA fingerprinting is restricted to the detection of microsatellites • 1 to 6 nucleotide repeats dispersed throughout the chromosomes • Probes used to identify the microsatellite surround the specific microsatellite being analyzed • Also called short tandem repeats (STR) • FBI has chosen 13 unique STRs for testing • Combined DNA Index System (CODIS)

  9. 8.3 Preparing a DNA Fingerprint • Specimen Collection • Search for sources of DNA • 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

  10. 8.3 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

  11. 8.3 Preparing a DNA Fingerprint • Extraction of DNA • DNA can be purified • Chemically (using detergents) • Mechanically (pressure to force DNA out of cell)

  12. 8.3 Preparing a DNA Fingerprint • RFLP Analysis • Treat DNA with restriction enzyme • Restriction enzyme cuts DNA at restriction sites • Use several restriction enzymes in sequence or combined • Use agarose gel electrophoresis to separate the pieces • Gel is chemically treated or heated to denature the DNA • Allows the binding of a single-stranded probe

  13. 8.3 Preparing a DNA Fingerprint • Southern Blot Technique • Transfer DNA fragments from gel to nitrocellulose or nylon membrane • Membrane incubated with a probe • Short strand of complementary DNA with a radioactive or fluorescent tag • Targeted area on the DNA fragment is called a locus • Expose X-ray (photo) film to membrane to obtain permanent record of results

  14. 8.3 Preparing a DNA Fingerprint

  15. 8.3 Preparing a DNA Fingerprint • PCR – used to amplify DNA found at crime scene into an amount that can be analyzed • DNA produced is identical to the original sample • Use amplified DNA in a Dot Blot Analysis • DNA amplified by PCR is blotted onto specially prepared blot strips • Each dot on the strip is a different DNA probe from human DNA

  16. 8.3 Preparing a DNA Fingerprint

  17. 8.3 Preparing a DNA Fingerprint • STR Analysis • Use primers to amplify STR’s in DNA using PCR • FBI uses 13 STR regions • Odds that two individuals will have the same 13-loci DNA profile are more than one in a billion

  18. 8.4 Putting DNA to Use • DNA fingerprinting is a comparative process • Looking for alignment of bands or dots in the fingerprint • All 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

  19. 8.4 Putting DNA to Use

  20. 8.4 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

  21. 8.4 Putting DNA to Use • Forest Hills Rapist • DNA first used in United States – 1987 • Victor Lopez tried for the sexual assault of three women • Reported assailant was a black man; Lopez was not a black man • DNA was a match to crime scene

  22. 8.4 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

  23. 8.4 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

  24. 8.4 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

  25. 8.4 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

  26. 8.5 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

  27. 8.5 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

  28. 8.5 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

  29. 8.6 Familial Relationships and DNA Profiles • Paternity Testing • Analyze samples from child and adults involved • Mitochondrial DNA • Used to examine samples that cannot be analyzed by PCR or RFLP • Older samples that lack nucleated cellular material (hair, bones, and teeth) • Inherited from the mother only • Changes only about 1% every million years due to random mutation

  30. 8.6 Familial Relationships and DNA Profiles

  31. 8.6 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

  32. 8.7 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 dinstinction appellation d’origine contrôlée in France • DNA evidence determined that the ancestors of cabernet sauvignon grapes are cabernet franc and sauvignon blanc

  33. 8.7 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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