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DNA & Blood Spatter Analysis Blood Splatter • • • When a wound is inflicted, a blood splatter pattern may be created. A group of blood stains makes a blood splatter pattern. Used to reconstruct the events surrounding a shooting, stabbing, or beating. Blood Splatter Analysis Analysis of a splatter pattern can aid in determining the: – direction blood traveled. – angle of impact. – point of origin of the blood. – velocity of the blood. – manner of death. Blood Splatter Analysis • Satellite droplets – blood falls from a height or at a high velocity – it can overcome its natural cohesiveness • Spiking pattern – Blood falls onto a less-thansmooth surface, Blood Splatter Analysis—Six Patterns Describe each of these: a. passive drops b. arterial gushes c. splashes d. smears e. trails f. pools Blood Splatter Analysis— Impact Patterns can help investigators determine the type of weapon used. Blood Splatter Analysis— Directionality The shape of an individual drop of blood provides clues to the direction from where the blood originated. Blood Splatter Analysis—Location of the Origin of the Blood Lines of convergence • Draw straight lines down the axis of the blood splatters. • Where the lines converge, the blood originated. Crime Scene Investigation of Blood 1. Search for blood evidence. 2. If any is discovered, process it determining: a. Whether the evidence is blood. b. Whether the blood is human. c. The blood type. 3. Interpret the findings: a. See if the blood type matches a suspect. b. If it does not, exclude that suspect. c. If it does, decide if DNA profiling is needed. Forensic Serology & DNA • The examination and analysis of the properties and effects of body fluids – Used primarily as screening tool • DNA analysis: identification • Biological evidence includes: – Blood, semen, saliva, sweat, urine, fecal matter – Bone, tissue, fingernail clippings Analysis of Biological Stains • Visual Examination/ Enhancement – Crime Scenes ( in situ) • Locate visible stains characteristic of blood or other fluids – Locating & defining areas of stain • Alternate light sources (black light) – Blood Enhancement chemicals • Not specific • Chemiluminescence or Fluorescence • Presumptive Tests – – – – – Easy Quick Very sensitive Crime scenes & Laboratory Not very specific (false positives) Identification of Blood • Most blood tests rely on characteristics of hemoglobin – Heme • Large ring structure with Fe at center – Peroxidase Peroxidase-like activity of heme • Provides catalyst for oxidation of normally colorless substrates in presence of hydrogen peroxide Uses of DNA Analysis • Paternity testing – identifying father • Historical investigations • Missing persons investigations • Mass disasters – putting pieces back together • Military DNA “dog tag” • Domestic Species ID • Forensic cases – matching suspect with evidence • Convicted felon DNA databases Steps in DNA Processing • Sample obtained – Crime scene or sample • DNA Extraction – Removed DNA from cells • DNA Quantification – How much DNA is present • DNA Analysis – PCR – Addition of dyes or probes • DNA Separation & Detection • Analysis of genomic results PCR • Polymerase Chain Reaction • Allows for exponential copies of DNA • Developed by Dr. Kary Mullis (a GT grad) Since we are all human. . . • Most of our DNA is alike • Non-coding regions – Not coding for genes – Unique – Certain areas of genome selected called loci • Combinations of loci selected DNA Separation • Separate DNA based on size of fragment • Detection using probes or dyes • Common analytical schemes – Gel electrophoresis – Capillary electrophoresis – Future technology • Polymers • Micro chips Gel Electrophoresis Capillary Electrophoresis Is it a match? • DNA isn’t reported as “matching” – A sample is included or excluded as a possible donor • Exclusions are relatively straightforward – genetic marker could not have originated from a specific individual, that individual is excluded as the donor • Inclusion can be far less exact – An individual may be included among those who could have generated evidence, but that can be from one to millions or billions of people CODIS • Combined DNA Index System – 7,434,897 offender profiles – 285,425 forensic profiles • Local, State, National Levels – Similar to AFIS • Compares DNA at 13 loci – The odds of 2 unrelated individuals matching at all 13 loci < 1 in 100 trillion – The earth’s human population is about 6 billion DNA v mtDNA • Nuclear DNA – Unique – Found in nucleus of cells • Mitochondrial DNA – Passed by mother – Used if necessary – Found in bones, hair; places where DNA is degraded or not present