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Forenisc identification John J. O’Leary MD, PhD, MSc, MA, FRCPath, FFPathRCPI, FTCD.

Forenisc identification John J. O’Leary MD, PhD, MSc, MA, FRCPath, FFPathRCPI, FTCD. Trinity College Dublin. Topics. Friction ridge identification Forensic dentistry Facial recognition and re-construction systems DNA fingerprinting. Forensic identification.

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Forenisc identification John J. O’Leary MD, PhD, MSc, MA, FRCPath, FFPathRCPI, FTCD.

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  1. Forenisc identification • John J. O’Leary • MD, PhD, MSc, MA, FRCPath, FFPathRCPI, FTCD. • Trinity College Dublin

  2. Topics • Friction ridge identification • Forensic dentistry • Facial recognition and re-construction systems • DNA fingerprinting

  3. Forensic identification • People can be identified by their fingerprints. We know this due to the philosophy of Friction Ridge Identification which states: "Friction ridge identification is established through the agreement of friction ridge formations, in sequence, having sufficient uniqueness to individualize". Friction ridge identification is also governed by four premises or statements of fact:

  4. Friction ridges 1. Friction ridges develop on the fetus in their definitive form prior to birth. 2. Friction ridges are persistent throughout life except for permanent scarring, disease or decomposition after death. 3. Friction ridge paths and the details in small areas of friction ridges are unique and never repeated. 4. Overall friction ridge patterns vary within limits which allow for classification.

  5. Fingerprints Arch Loop Whorl Arch – tented arch

  6. Fingerprints

  7. Forensic dentistry • Forensic dentistry or forensic odontology is the proper handling, examination and evaluation of dental evidence. The evidence that may be derived from teeth, is the age (in children) and identification of the person to whom the teeth belong. This is done using dental records or ante-mortem (prior to death) photographs.

  8. Facial recognition system • A facial recognition system is a computer application for automatically identifying or verifying a person from a digital image or a video frame from a video source. One of the ways to do this is by comparing selected facial features from the image and a facial database.

  9. Facial recognition and reconstruction

  10. DNA fingerprinting

  11. DNA forensics • DNA • Chromosomes • Nucleotides • Adenosine (A) • Guanine (G) • Cytosine (C) • Thymidine (T)

  12. The structure of DNA

  13. The structure of DNA

  14. The structure of DNA

  15. Every chromosome has a unique signature

  16. The sequence of DNA

  17. DNA Protein RNA DNA-RNA-Protein

  18. What is DNA? • DNA is the chemical substance which makes up our chromosomes and controls all inheritable traits (eye, hair and skin color) • DNA is different for every individual except identical twins • DNA is found in all cells with a nucleus (white blood cells, soft tissue cells, bone cells, hair root cells and spermatozoa) • Half of a individual’s DNA/chromosomes come from the father & the other half from the mother.

  19. DNA Review: • DNA is a double-stranded molecule. • The DNA strands are made of four different building blocks. • An individual’s DNA remains the same throughout life. • In specific regions on a DNA strand each person has a unique sequence of DNA or genetic code.

  20. Chromosome facts • Number of chromosome = 46 • 22 autosomes and 2 sex chromosomes • One chromosome of each pair donated from parents sperm or egg • Sex chromosomes • XY male: XX female • Largest chromosome: chr 1-263 million base pairs (bp) • Smallest chromosome: chr Y - 59 million base pairs (bp)

  21. Gene facts • Human genome = 3.4 billion base pairs • Number of human genes: approx 100,000 • Genes vary in length: average 3,000 bp • Only 5% of human genome is coding and contains genes • Genes divided into exons and introns • Much of the function of the genome unknown • 0.1% difference in DNA between individuals

  22. Gene facts: repetitive genome units • Minisatellites are molecular marker loci consisting of tandem repeat units of a 10-50 base motif, flanked by conserved endonuclease restriction sites • DNA fingerprinting • VNTR (Variable Number of Tandem Repeats) • Microsatellites are simple sequence tandem repeats (SSTRs). The repeat units are generally di-, tri- tetra- or pentanucleotides. For example, a common repeat motif in birds is ACn, where the two nucleotides A and C are repeated in bead-like fashion a variable number of times (n could range from 8 to 50) • Simple sequence repeats (SSR) • Simple sequence length polymorphisms (SSLP)

  23. Other important gene regions • Single nucleotide polymorphisms or SNPs (pronounced "snips") are DNA sequence variations that occur when a single nucleotide (A,T,C,or G) in the genome sequence is altered. For example a SNP might change the DNA sequence AAGGCTAA to ATGGCTAA. • For a variation to be considered a SNP, it must occur in at least 1% of the population. • SNPs, which make up about 90% of all human genetic variation, occur every 100 to 300 bases along the 3-billion-base human genome

  24. Use of DNA forensics • Identification purposes • Identify crime suspects • Exonerate persons wrongly accused of crime • Identify crime and catastrophe victims • Establish paternity and other family relationships

  25. Factors Leading to DNA Degradation • Time • Temperature • Humidity • Light • Exposure to chemicals

  26. DNA as Physical Evidence • Perspective • Recognition of Evidence • Collection of Physical Evidence • Preservation of Physical Evidence • Preparation of the Physical Evidence • Evaluation and Quantification of the Evidence

  27. Individualization: • Evidence that exhibit traits that are are so unique that when considered alone or in combination with other traits can reduce the evidence source from a class to one individual. • Evidence that can indicate that two samples share a common unique source or origin.

  28. Association: • “Description of the relationship between two objects items, or people.” • Concept used in a crime scene analysis for reconstruction. • “Involves the evaluation of evidence to infer a common source.” • Does not prove a crime.

  29. Traits that Indicate Individuality • Fingerprints - are a result of several genes and other non-genetic events. Has been accepted as unique for each individual (even identical twins) • DNA - early results suggested individuality except in identical twins; but in reality more like a partial print.

  30. Sources of DNA for Testing • Blood • Semen • Tissue • Bone (Marrow) • Hair Root • Saliva • Urine • Tooth (Pulp)

  31. How is DNA typing done • Strict anti-contamination procedures • Standard operating procedure for every forensic DNA test • Dedicated laboratory facilities • Contact DNA tracing

  32. DNA technologies used in forensic investigations • RFLP • PCR-RFLP • STR analysis • Mitochondrial DNA (mtDNA) • Y-chromosome analysis • SNP genotyping

  33. DNA technologies used in forensic investigations • RFLP • PCR-RFLP • VNTRs • HLA-DQ • STR analysis • Mitochondrial DNA (mtDNA) • Y-chromosome analysis • SNP genotyping

  34. Basis of RFLP analysis • Restriction Enzymes (biological catalysts) cut DNA whenever they encounter a specific DNA sequence. • Gel electrophoresis separates the fragments of DNA according to their length.

  35. Basis of RFLP analysis

  36. Basis of RFLP analysis

  37. A Schematic Representation of RFLP and Southern Blot of a Single-locus VNTR

  38. In the segment of DNA shown below, you can see the elements of an RFLP: a target sequence flanked by a pair of restriction sites. When this segment of DNA is cut by EcoR I, three restriction fragments are produced, but only one contains the target sequence which can be bound by the complementary probe sequence (purple).

  39. Let's look at two people and the segments of DNA they carry that contain this RFLP (for clarity, we will only see one of the two stands of DNA). Since Jack and Jill are both diploid organisms, they have two copies of this RFLP. When we examine one copy from Jack and one copy from Jill, we see that they are identical: Jack 1: -GAATTC---(8.2 kb)---GCATGCATGCATGCATGCAT---(4.2 kb)---GAATTC- Jill 1: -GAATTC---(8.2 kb)---GCATGCATGCATGCATGCAT---(4.2 kb)---GAATTC-

  40. When we examine their second copies of this RFLP, we see that they are not identical. Jack 2 lacks an EcoR I restriction site that Jill has 1.2 kb upstream of the target sequence (difference in italics). Jack 2: -GAATTC--(1.8 kb)-CCCTTT--(1.2 kb)--GCATGCATGCATGCATGCAT--(1.3 kb)-GAATTC-Jill 2: -GAATTC--(1.8 kb)-GAATTC--(1.2 kb)--GCATGCATGCATGCATGCAT--(1.3 kb)-GAATTC-

  41. RFLP analysis

  42. Use of optimum number of loci for RFLP analysis

  43. DNA technologies used in forensic investigations • RFLP • PCR-RFLP • VNTRs • HLA-DQ • STR analysis • Mitochondrial DNA (mtDNA) • Y-chromosome analysis • SNP genotyping

  44. Polymerase Chain Reaction (PCR) PCR -RFLP

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