Forensic Dna Me


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Forensic Dna Me

  1. 1. The Indispensable Forensic Science Tool DNA:
  2. 2. Why is DNA an Indispensable Tool Forensic Science? <ul><li>Study into the structure of the human genome has led to the discovery that portions of the DNA structure of certain genes are as unique to each individual as fingerprints </li></ul>
  3. 3. <ul><li>Part I. What is DNA </li></ul><ul><li>Part II. DNA Profiling </li></ul><ul><li>Part III. DNA Testing </li></ul>
  4. 4. Its Uses <ul><li>Identification of remains </li></ul>
  5. 5. The Angel of Death: Josef Menegle <ul><li>Josef Mengele was a Nazi war criminal notorious for grotesque human experiments in concentration camps. </li></ul><ul><li>After the Second World War he fled to South America living out the rest of his days without being caught. </li></ul><ul><li>In 1985 investigators went to the cemetery of Nossa Senhora do Rosario in the small Brazilian town of Embu to dig up the skeleton of a man who had been drowned in a swimming accident six years previously. </li></ul><ul><li>Using DNA extracted from blood provided by Mengele’s wife and son, it was concluded that it was more than 99.94% certain that the skeleton was Mengele’s. </li></ul>
  6. 6. Paternity Cases <ul><li>Who’s your daddy? </li></ul>1. 2. 1. 2.
  7. 7. Homicide or Rapes: OJ Simpson
  8. 8. Exoneration <ul><li>Kirk Bloodsworth </li></ul><ul><ul><li>Convicted in 1985 for the rape and strangulation of a 9-year old girl and sent to death row </li></ul></ul><ul><ul><li>In 1992, defense attorneys were successful in having a dime-sized semen stain on the girl’s underpants tested against Bloodsworth’s DNA </li></ul></ul><ul><ul><li>He was exonerated </li></ul></ul>
  9. 9. Exoneration
  10. 10. What is DNA? <ul><li>Each of our 60 trillion cells contains nuclear genetic material called chromosomes </li></ul><ul><ul><li>Arranged on these chromosomes are genes </li></ul></ul><ul><ul><ul><li>Which are used to make proteins (example: hair color or susceptibility to diseases is determined by these proteins) . </li></ul></ul></ul>
  11. 11. James Watson & Francis Crick <ul><li>1953 discovered the structure of Deoxyribonucleic Acid – DNA </li></ul><ul><ul><li>Double Helix </li></ul></ul><ul><ul><li>Composed of 4 different type bases </li></ul></ul><ul><ul><ul><li>complementary base pairing of Adenine always with Thymine and Guanine with Cytosine. </li></ul></ul></ul>
  12. 12. What is DNA? <ul><li>Made from repeating nucleotides. </li></ul><ul><ul><li>DNA nucleotides are composed of a sugar molecule, a phosphate group, and a nitrogen base. </li></ul></ul>
  13. 13. <ul><li>The backbone of the DNA chain is supported by the phosphorous and sugar groups – forming the rungs of the “ladder” </li></ul>
  14. 14. A T A G C C A A C C A A T A T C G G T T G G T T Replication of a single strand of DNA
  15. 15. DNA at Work <ul><li>DNA controls the production of Proteins </li></ul><ul><ul><li>Proteins are polymers of amino acids </li></ul></ul><ul><ul><li>There are 20 known amino acids yet thousands of different proteins can be produced performing different functions. </li></ul></ul>
  16. 16. How can the DNA sequence dictate the sequence for a particular protein? <ul><li>DNA is a template used by RNA to construct a protein </li></ul><ul><li>Thymine on the DNA nucleotide is replaced by Uracil on the RNA nucleotide so A is paired with U. </li></ul><ul><li>Each amino acid is attached to a triplet complementary codon of a RNA transcribed DNA sequence. </li></ul>
  17. 17. U A U C G G U U G G U U A T A G C C A A C C A A So, a DNA Sequence of: Would have an mRNA sequence of : Use the following table to determine which of the 20 amino acids would make up this sequence. Each group of three nucleotide bases, an RNA triplet codon, is read in order to determine which amino acid is placed in the sequence. The sequence determines the type of protein that is produced. U A U C G G U U G G U U DNA template Strand RNA Strand of Transcribed DNA
  18. 18. U A U C G G U U G G U U
  19. 19. U A U C G G U U G G U U mRNA Sequence: Would result in this protein amino acid sequence Tyrosine Arginine Leucine Valine Tyrosine Arginine Leucine Valine
  20. 20. U A U C G G U U C G U U a one base change in the mRNA Sequence: Would result in this protein amino acid sequence U A U C G G U U G G U U Tyrosine Arginine Phenylalaine Valine Tyrosine Arginine Phenylalaine Valine
  21. 21. II. DNA Profiling <ul><li>“ I didn’t understand the DNA stuff at all. To me, it was just a waste of time. It was way out there and carried absolutely no weight with me at all.” </li></ul><ul><li>Post-trial commentary from a juror in the O.J. Simpson trial: V. Bugliosi, Outrage (New York: Dell Publishing, 1996). </li></ul><ul><li>“ In a forensic setting, ... an innocent suspect has little to fear from DNA evidence, unless he or she has an evil twin.” </li></ul><ul><li>N. Risch & B. Devlin, “On the Probability of Matching DNA Fingerprints” (1992) 255 Science. </li></ul>
  22. 22. Discovery – Sir Alec Jeffreys <ul><li>Discovered in 1984 by Dr. Alec Jeffreys at the university of Leicester </li></ul><ul><li>Was knighted for his discovery </li></ul>
  23. 23. DNA Analysis A New Technique –- Why Use It? <ul><li>DNA Analysis is useful because : </li></ul><ul><ul><li>The DNA contains “detectable” patterns unique to each individual </li></ul></ul><ul><ul><li>DNA can be isolated from a wide range of biological samples likely present at a crime scene </li></ul></ul><ul><ul><li>The source of DNA doesn’t matter – it is the same in all sources (blood, semen, sputum, skin etc) </li></ul></ul><ul><ul><li>Methods are fast and relatively cheap </li></ul></ul><ul><ul><li>Data are complied in databases, and are easily searched </li></ul></ul>
  24. 24. How Does It Work? <ul><li>Biology 101 : </li></ul><ul><ul><li>Every cell in your body contains DNA (except sperm/eggs) </li></ul></ul><ul><ul><li>DNA is unique to each individual: even though we share 99.9% of our genome in common with other humans, 0.1% </li></ul></ul><ul><ul><li>The challenge: find the differences! </li></ul></ul>
  25. 25. Potential Sources of DNA <ul><li>Blood (White blood cells) </li></ul><ul><li>Semen (Sperm cells) </li></ul><ul><li>Hair with roots (Hair follicle cells) </li></ul><ul><li>Skin, dandruff (Skin cells) </li></ul><ul><li>Sweat stains (Skin cells sloughed off) </li></ul><ul><li>Vaginal fluids (Mucosal surfaces) </li></ul><ul><li>Nasal secretions (Mucosal surfaces) </li></ul><ul><li>Urine (Mucosal surfaces) </li></ul><ul><li>Feces (Digestive system cells) </li></ul>
  26. 26. The 2 Main Types of DNA Profiling <ul><li>R estriction F ragment L ength P olymorphisms (RFLPs) </li></ul><ul><ul><li>R estriction from the enzymes that cut the DNA (restriction enzymes) </li></ul></ul><ul><ul><li>F ragment for the fragments produced by the cutting </li></ul></ul><ul><ul><li>L ength and P olymorphisms for the different sized fragments produced (polymorphic = many forms) </li></ul></ul><ul><li>S hort T andem R epeats (STRs) </li></ul><ul><ul><li>Short because the differences are short – usually 1-4 nucleotides in length </li></ul></ul><ul><ul><li>Tandem because they occur one after the other </li></ul></ul><ul><ul><li>Repeats because they are repeats of the same DNA sequence </li></ul></ul><ul><ul><li>e.g. ACTG- GCC- GCC-GCC-GCC-ATCGACC = 4 tandem repeats of GCC </li></ul></ul>
  27. 28. 1. RFLPs <ul><li>DNA is cut by molecular “scissors” – enzymes which recognize particular sequences of nucleotides </li></ul><ul><li>These enzymes identify short sequences of DNA, then snip it </li></ul><ul><li>Because everyone’s DNA is different, enzymes cut in different places </li></ul><ul><li>The resulting samples contain DNA fragments of different size ( R estriction F ragment L ength P olymorphisms) </li></ul>
  28. 29. RFLP: Electrophoresis <ul><li>DNA is visualized using electrophoresis </li></ul><ul><li>Negatively charged DNA moves through a gel with a current </li></ul><ul><li>Smaller DNA moves faster than larger DNA fragments </li></ul>
  29. 30. RFLP: Autoradiograph
  30. 31. <ul><li>The DNA fingerprint from suspect 1 matches up with the fingerprint of the sperm DNA from the crime scene. You can also see that the female cells from the scene match the victim’s DNA. </li></ul>
  31. 32. How unique are these profiles? <ul><li>The probability of 2 people having exactly the same DNA profile is between </li></ul><ul><li>1 in 5 million to </li></ul><ul><li>1 in 100 billion </li></ul><ul><li>(greater than the population of humans on earth) </li></ul><ul><li>This number becomes even larger if you consider more regions of DNA </li></ul><ul><li>Thus, the odds that the DNA evidence from a crime scene will match your DNA profile is astronomically small (unless you have an evil identical twin) </li></ul>
  32. 33. Paternity <ul><li>DNA fingerprinting can be used to identify a child’s parents. Each child inherits one set of chromosomes from each parent. </li></ul><ul><li>Some RFLPs are inherited from the mother and some from the father. </li></ul>
  33. 34. Interpret the results of the following DNA fingerprints <ul><li>B oth daughter 1 and son 1 share RFLPs with both the mom and dad, while daughter 2 has RFLPs of the mom but not the dad, and son 2 does not have RFLPs from either parent. </li></ul>
  34. 35. <ul><li>The police use the same analysis to determine the identity of a person at a crime scene. After collecting DNA samples from the scene and any suspects, the police amplify and digest the DNA with a restriction enzyme. The samples are run on an agarose gel, and the bands found at the crime scene are aligned with those of the suspects’. </li></ul>
  35. 36. 2. STRs <ul><li>Much of the process of collecting STR data has been automated, including gel electrophoresis </li></ul><ul><li>To collect and analyze STR evidence, copies of the variables regions of the DNA are amplified (millions of copies are made) </li></ul><ul><li>The DNA is then fed through a machine that reads the DNA by size – a laser scans and detects the stained DNA samples as they electrophorese through the machine </li></ul>
  36. 42. How do we get so much variation? Recall inheritance patterns...
  37. 43. How do we get so much variation? Recall inheritance patterns... <ul><li>In this example, there are 4 types of offspring possible for the parents with their genotypes; </li></ul><ul><li>6,8 </li></ul><ul><li>6,2 </li></ul><ul><li>3,8 </li></ul><ul><li>3,2 </li></ul>
  38. 44. Automated STR Test
  39. 45. Crime Scene Samples & Reference Samples <ul><li>Differential extraction in sex assault cases separates out DNA from sperm cells </li></ul><ul><li>Extract and purify DNA </li></ul>
  40. 46. Extract and Purify DNA <ul><li>Reactions are performed in Eppendorf tubes. Typical volumes are measured in microliters (one millionth of a liter). </li></ul>
  41. 47. PCR Amplification <ul><li>Groups of amplified STR products are labeled with different colored dyes (blue, green, yellow) </li></ul><ul><li>DNA regions flanked by primers are amplified </li></ul>
  42. 49. Genetic Analyzer: SIZE, COLOR & AMOUNT
  43. 50. Genetic Analyzer: Capillary Electrophoresis <ul><li>Amplified STR DNA injected onto column </li></ul><ul><li>Electric current applied </li></ul><ul><li>DNA separated out by size: </li></ul><ul><ul><li>Large STRs travel slower </li></ul></ul><ul><ul><li>Small STRs travel faster </li></ul></ul><ul><li>DNA pulled towards the positive electrode </li></ul><ul><li>Color of STR detected and recorded as it passes the detector </li></ul>Detector Window