Serology

  • Typing of Dried Blood Stains: Absorption-elution technique
    • Antiserum on blood stain causes antibodies to mix with specific antigens
    • Unrated serum is washed off
    • Elution: breaking of antibody-antigen bond
    • Known rbcs are added
    • Agglutination will occur if antigens on RBCs were also on the stained material
  • Differentiating Blood Types
    • Enzymes: proteins that speed up or slow down chemical reactions
    • Enzymes that exist in different forms are called polymorphic and can be broken down into their separate proteins (iso-enzymes)
    • Phenotypes
    • PGM: electrophoresis can separate the protein components into iso-enzymes
    • EAP: determined by the intensity of the fluorescence
      • The darker the band, the more it fluoresces
  • Bloodstain Spatter
    • A blood droplet will remain spherical in the air
    • Once a blood droplet impacts a surface, a bloodstain is formed
    • Two droplets falling from the same height and angle and hitting the same surface will produce the same shape
    • Bloodstains as evidence:
    • Origins of bloodstain
    • Distance of bloodstain from target
    • Direction from which blood impacted
    • Speed with which blood left its source
    • Position and movement of victim and assailant
    • Number of blows/shots
    • Droplet Volume
    • Directly dependent upon the place it originates from
    • The impact area is called the target surface
    • Volume is from 0.03-0.15 cc
    • Shape is effected by size, angle, velocity, and texture
    • On clean glass or plastic, the droplet will have smooth outside edges
    • On rough surfaces, the droplet with have scalloped edges
    • Bloodstains show:
    • Movement and direction of a person or an object
    • Number of blows/shots/etc.
    • Type and direction of impact
  • Bloodstain Patterns
    • circumstantial evidence
    • Shape
    • Round if it falls at a 90 degree angle
    • Elliptical: blood droplet elongates as the angle decreases from 90 to 0 degrees
    • Impact angle = sin^-1(arcsin) (width/length)
    • Impact
    • Overall direction of blood flow can be determined by impact shape
    • The more acute the angle, the more elongated the stain, the easier it is to determine the direction
    • At about 30 degrees the stain will begin to produce a tail
    • Breaking
    • The harder the surface, the less the drop will break apart (less porous)
    • The softer the surface, the more the drop will break apart (more porous)
    • Pointed end of the blood stain faces the direction the stain is traveling
    • Point/Area of Convergence: location of the blood source can be determined by drawing lines connecting the various blood droplets
    • Point of Origin:
    • above the point of convergence; the spot where the blow occurred
    • Determined by drawing a line straight up from the angle of convergence to where the angle of impact
  • Semen
    • Sperm
    • One of the smallest and most highly specialized cells in the human body
    • Has a head and a tail
    • Contains 23 chromosomes w the genetic material found in the head
    • Determination of seminal fluid:
    • Acid phosphatase color test
      • The enzyme secreted by the prostate gland into the seminal fluid will turn purple
      • Will fluoresce under UV light
    • Prostate Specific Antigen (PSA) or p30
      • P30 is isolated and injected into a rabbit where antibodies are produced
      • Antigens and antibodies move toward each other
      • Formation of a precipitation line shows presence of p30
      • Must be seminal fluid