Biological Evidence I Serology
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Biological Evidence I Serology

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    Biological Evidence I Serology Biological Evidence I Serology Presentation Transcript

    • Chapter 9
    • Blood and Physiological Fluid Evidence: Evaluation and Initial Examination
      • How Biological Evidence Analysis Has Changed Because of DNA Typing
      • Nature of Blood
      • Collection, Preservation, and Packaging of Biological Evidence
      • Test Controls, Substratum Comparison Specimens, and Contamination Issues
      • Initial Examination of and for Biological Evidence
      • Forensic Identification of Blood
      • Species Determination
      • Forensic Identification of Body Fluids
      • Forensic Investigation of Sexual Assault Cases
      • Blood and Body Fluid Individuality: Traditional Approaches
    • I. How Biological Evidence Analysis has Changed Because of DNA Typing
      • Prior to the introduction of forensic DNA typing analysis, blood groups were the genetic markers that were analyzed from biological evidence (forensic serology)
      • Forensic biology now refers to the preliminary examination of biological evidence prior to the DNA typing analysis procedures
    • II. Nature of Blood
      • Blood contains cells, nutrients, chemical messengers, and ingested substances
      • A tube of whole blood will clot producing two fractions: a yellow serum layer and a dark red clot containing cellular material
      • Anticoagulants prevent blood clotting yielding a yellow plasma layer and a cell fraction that settles to the bottom of the tube
    • II. Nature of Blood
      • The cellular fraction of blood contains red blood cells (erythrocytes) and white blood cells (leucocytes)
      • White blood cells are the source of DNA for DNA typing analysis
      • Red blood cells do not contain any nuclear DNA
    • III. Collection, Preservation, and Packaging of Biological Evidence
      • Blood or Buccal Swabs from Known Person:
      • Blood is drawn into a vacutainer tube containing an anticoagulant such as EDTA (“purple top” tube)
      • Buccal (cheek) swabs are often used in place of liquid blood as the known sample
    • III. Collection, Preservation, and Packaging of Biological Evidence
      • Biological Evidence from Scenes:
      • Fresh or web blood should be collected on clean, sterile, gauze and allowed to dry
      • Four sampling methods for dried blood:
        • Cutting – For stains on objects that are difficult to submit to the lab. The cut portion should include unstained areas around the bloodstain
        • Swabbing – Stain is transferred to a swab which has been moistened with sterile water or saline.
        • Scraping – a sharp instrument is used to scrape the stain off of a surface & onto clean paper
        • Elution – using a small amount of saline or distilled water to dissolve the dried stain
    • III. Collection, Preservation, and Packaging of Biological Evidence
      • The most important consideration for preserving biological evidence from scenes is to thoroughly dry the item before packaging and then store in a cool dry environment
      • Biological evidence must be packaged in paper containers that can breathe
    • IV. Test Controls, Substratum Comparison Specimens, and Contamination Issues
      • 1. Known (Exemplar or Reference) Control:
        • are specimens from a known source
        • essential for comparison with DNA profiles from evidentiary specimens
      • 2. Alibi (Alternative) Known Control:
        • From a known source that may be the source of the evidence
      • 3. Blank Control:
        • A specimen known to be free of the item or substance being tested
    • IV. Test Controls, Substratum Comparison Specimens, and Contamination Issues
      • 4. Substratum Comparison Specimens:
      • Substratum refers to the underlying material or surface on which the evidence is found
      • A substratum comparison specimen is subjected to the same testing as the evidence
      • The specimen helps to detect interference in lab tests originating from the evidence surface
      • An unstained portion of the evidence underlying material is collected for this purpose
    • IV. Test Controls, Substratum Comparison Specimens, and Contamination Issues
      • Evidence may be contaminated in several ways:
        • Biological material may have been on a surface before the biological evidence was deposited
        • During scene searching &/or processing activities
        • During laboratory examinations &/or manipulations
    • V. Initial Examination of and for Biological Evidence
      • The initial examination is designed to evaluate stains for possible evidentiary value
      • Activities include:
        • Searching for biological stains
        • Preliminary tests for physiological fluids
        • Positive preliminary tests are then subjected to confirmatory tests
        • Cutting out or transferring stains to swabs for subsequent examinations
    • VI. Forensic Identification of Blood
      • Two categories of identification tests:
      • Presumptive or preliminary test
        • Used for screening specimens that might contain the substance or material of interest
        • Both false positive and false negative results may be obtained
      • Confirmatory test
        • Are tests which are entirely specific for the substance or material for which it is intended
        • A positive confirmatory test is interpreted as an unequivocal demonstration that the specimen contains the substance or material
    • VI. Forensic Identification of Blood
      • Presumptive Tests for Blood:
      • Presumptive blood tests are used to screen evidence for the possible presence of blood
      • Most are color tests and are based on the peroxidase-like activity of hemoglobin
      • Peroxidase catalyzes the following reaction
      • Reduced Dye + peroxide --> Oxidized dye + water
      • The presence of hemoglobin catalyzes the reaction, forming a colored dye product
      • Positive presumptive tests do not prove that blood is present
    • VI. Forensic Identification of Blood
      • Confirmatory Tests for Blood:
      • Older tests included crystal tests such as the Teichmann and Takayama tests
      • Current immunological tests use antibodies specific for human hemoglobin, thus combining the confirmatory test for blood with a human species test
      • The crystal tests and the immunological tests are known as direct confirmatory tests
    • VII. Species Determination
      • Tests must be done on blood specimens to determine the species of origin
      • Species origin tests are done using immunological methods which involve the interaction of antigens and antibodies
      • Hemoglobin from human red blood cells can be used as the antigen to produce anti-human hemoglobin serum
      • Specific antiserum can be used to test for the presence of antigens in unknown specimens
    • VII. Species Determination
      • Common immunological species tests include the Ouchterlony method
      • Extracts of the bloodstain to be analyzed are tested with specific antisera
      • If the bloodstain contains the antigens corresponding to the specificity of the antiserum, a visible precipitate (precipitin) is obtained
    • VIII. Forensic Identification of Body Fluids
      • 1. Identification of Semen:
      • Semen is a mixture of specialized cells, called spermatozoa, suspended in a fluid known as seminal plasma
      • UV light causes semen stains to fluoresce, and is therefore used to locate stains
      • Both presumptive and confirmatory tests for semen stains are available
    • VIII. Forensic Identification of Body Fluids
      • Presumptive Test for Semen:
      • The AP test is a color test based on the detection of acid phosphatase, an enzyme from the prostate gland that is found in high concentration in human semen
      • Confirmatory Test for Semen:
      • A commonly used approach is to use a microscope to detect spermatozoa in smears made from dried stains
      • When no sperm are found, immunological methods are used to detect the presence of a prostate gland protein called p30 or PSA
    • VIII. Forensic Identification of Body Fluids
      • 2. Identification of Vaginal Secretions, Saliva, and Urine:
      • There are no reliable methods for identifying human vaginal material
      • Presumptive tests for saliva are based on the presence of the enzyme amylase
      • There are no confirmatory tests for saliva
      • Presumptive tests for urine are based on the presence of urea and creatinine
      • There are no confirmatory tests for urine
    • IX. Forensic Investigation of Sexual Assault Cases
      • 1. Coordination of Effort – SANEs and SARTs
      • The medical examination of complainants in sexual assault cases is performed by specially trained sexual assault nurse examiners (SANE)
      • Forensic nurses take a lead role in the coordinated response by the sexual assault response team (SART)
      • Complainants are taken to a medical facilities or a SANE/SART facility to attend to their medical needs and to collect relevant evidence using a sexual assault evidence collection kit (”rape kit”)
    • IX. Forensic Investigation of Sexual Assault Cases
      • 2. The Forensic Scientist’s Role:
      • Sexual assault evidence collection kits are forwarded to the forensic lab for examination
      • The forensic scientist’s primary role is the analysis of the physical evidence
      • If semen is present it helps to establish the corpus delicti
      • If semen or other fluids are found, DNA typing is conducted to determine if there is a match to a suspect or an exclusion
    • IX. Forensic Investigation of Sexual Assault Cases
      • 3. Medical Examination:
      • Medical evaluation and treatment of sexual assault victims initially involves recording the history of the events, tending to any injuries, and documenting any injuries, bruises, or contusions
      • This is followed by evidence collection, which includes clothing, vaginal swabs, pubic hair combings, any stains on the skin surface, and a known control (blood or buccal swab)
    • IX. Forensic Investigation of Sexual Assault Cases
      • 4. Sexual Assault Evidence Collection Kits:
      • Sexual assault evidence collection kits contain a variety of containers and envelopes plus a detailed set of instructions on how to use them
      • Not every container/envelope is used in every case
    • IX. Forensic Investigation of Sexual Assault Cases
      • 5. Types of Sexual Assault Cases
      • There are three types of sexual assault cases: unknown offender (identification cases), known offender (consent cases), and sexual assaults involving children
      • DNA profiling is helpful in identification cases but not in consent cases
      • State laws define the age of consent, thereby differentiating between an adult and child
    • IX. Forensic Investigation of Sexual Assault Cases
      • 6. Drug Facilitated Sexual Assault:
      • Several drugs are commonly encountered as “date rape” drugs: rohypnol, GHB, & ketamine
      • All are depressants with amnestic effects, and are often used along with alcohol
      • These types of cases require toxicological analysis of the evidence
      *Figure 9.7*
    • X. Blood and Body Fluid Individuality: Traditional Approaches
      • 1. The Classical or Conventional Genetic Markers:
      • 5 categories of classical genetic markers: blood groups, isoenzymes, plasma (serum) proteins, hemoglobin variants, and HLA
      • The first blood group markers were ABO, discovered in 1901 by Karl Landsteiner
      *Figure 9.9*
    • X. Blood and Body Fluid Individuality: Traditional Approaches
      • ABO markers were first applied to criminal cases involving bloodstains by Dr. Leon Lattes of Italy in 1913
      • Isoenzymes are enzymes which occur in multiple molecular forms, reflecting differences in the gene that code for the enzyme
      • Similarly, there are common variants of the protein hemoglobin
      *Figure 9.10*
    • X. Blood and Body Fluid Individuality: Traditional Approaches
      • 2. How Does Typing Genetic Markers Help “Individualize” a Biological Specimen?
      • A gene is a region of DNA that codes for a particular protein or enzyme
      • Because chromosomes are paired (maternal and paternal), and there is one gene on each chromosome, the genes are paired
      • A gene locus is the location on a chromosome where a particular trait is determined
    • X. Blood and Body Fluid Individuality: Traditional Approaches
      • The genes making up a pair at a given locus are called alleles
      • The alleles may be the same (homozygous) or different (heterozygous)
      • Population genetics looks at how often alleles found at a given locus occur in a population
      • A portion of a large population is sampled and tested to determine the frequency of a particular allele
      • Statistics are used to estimate the frequency of an allele in the entire population