Forensic Serology YouTube - The Sam Sheppard case
Introduction • 1901- Karl Landsteiner recognized that human blood was distinguishable by its group or type • Bloodstains are often found at crime scenes (homicides, assaults, rapes, etc.) • Blood Factors (like A-B-O, Rh factor, and others) have been used to link a crime to a suspect or a victim. • Since the early 1990’s, DNA technology has completely changed the way in which bloodstains and other biological evidence is individualized.
The Nature of Blood Blood is composed of : • Plasma- the fluid portion of unclotted blood • Red Blood Cells (erythrocytes) • White blood cells (leukocytes) • Platelets Serum-yellowish liquid that separates from blood when a clot has formed.
Antigens and Antibodies • Antigens-substances, usually proteins, found on the surface of red blood cells that give the cells specific characteristics • Antibodies-proteins found in blood serum that destroy or inactivate a specific antigen by binding to it. • Agglutination-clumping together of red blood cells cause by an antigen/antibody interaction • Serology-the study of antigen-antibody reactions
Blood Typing • Serology – the study of antigen-antibody reactions. Distribution of blood types in the U.S.:
Forensic Characterization of Bloodstains Bloodstains must be analyzed to determine: • Is it blood? • From what species did the blood originate? • How closely can it be associated with a particular individual?
Forensic Characterization of Bloodstains • Color Tests-Kastle-Meyer test-oxidation of hemoglobin in blood produces a deep pink color. • Luminol-reaction with blood produces light; faint blue glow known as luminescence; very sensitive technique • Immunoassays-Antigen-antibody reactions are used to identify blood and also detect drugs in blood
Forensic Characterization of Bloodstains • Microcyrstalline tests-Takayama and Teichmann tests; substances form crystals when they come in contact with hemoglobin; less sensitive than color tests • Precipitin test-used to detect human blood • Gel diffusion-another method for detecting human blood.