1 / 29

Chapter 12 FORENSIC SEROLOGY

Chapter 12 FORENSIC SEROLOGY. Questions to Ask. Is it blood? Is it animal or human? What is the blood type? What do blood stain patterns suggest? How can patterns help recreate the crime scene?. Ludwig Tessnow, 1901. Open area on Rugen Island, near where the children's bodies were found

dima
Download Presentation

Chapter 12 FORENSIC SEROLOGY

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 12FORENSIC SEROLOGY

  2. Questions to Ask • Is it blood? • Is it animal or human? • What is the blood type? • What do blood stain patterns suggest? • How can patterns help recreate the crime scene?

  3. Ludwig Tessnow, 1901 • Open area on Rugen Island, near where the children's bodies were found • Paul Uhlenhuth, biologist, could distinguish blood from other substances, as well as mark the difference between human and animal blood

  4. When wounded, bodies leak or spray blood, and the behavior of blood in flight tends to be unaffected by such things as temperature, humidity, or atmospheric pressure. In other words, it's uniform. • 1901 - Karl Landsteiner named and organized blood into groups (ABO/Rh)

  5. Blood and Blood Typing Blood makes up 8% of body by weight (5L) FIVE MAIN FUNCTIONS: • Main transportation system (O2/CO2, Chemical messengers) • Circulation of blood maintains body temperature • Maintains body's pH via CO2 levels (7.4) • Transports toxins to kidneys for excretion (filter 1.5 times per hour) • Control balance of body's electrolytes (salt)

  6. Blood Composition Mostly water • Erythrocytes (RBC) • Leukocytes (WBC) • Thrombocytes (Platelets) Layers • Plasma (top) – 92% water, 55% of blood! • Buffy Coat (creamy middle) – WBC/Platelets • Dense Layer – RBC (45% of blood)

  7. Who cares what's in there?! • RBC – Hemoglobin for Oxygen • WBC – Immune system Antigens are PROTEIN TAGS that tell your blood type

  8. What's your type? Antigens (show what you are) • A • B • O (lack of A or B antigens) • Rh (Presence known as +, absence as -) Antibodies (against what you aren't) • A antibody (binds to A antigen causing clumping) • B antibody (binds to B antigen causing clumping) • O (This type of blood has both A and B antibodies!) • Rh (binds to Rh antigen causing clumping) CLUMPING = AGGLUTINATION = BAD NEWS

  9. Karl Landsteiner, 1901 • Received Nobel Prize for Blood Typing, ABO blood groups • Blood transfers now successful! • Direct blood typing – liquid state

  10. Leone Lattes • Developed method for typing DRIED blood • Indirect bloody typing – Dried • Used on Egyptian mummies • Absorption-elution method (reconstituted in saline)

  11. Is it blood? Benzidine and phenolphthalein + blood = red Benzidine and peroxidase + blood = blue Luminol – glows in the dark (most sensitive 1:5,000,000) • False positives: horseradishes, radishes, oranges, lemons, grapefruit

  12. Is it human? Precipitin Test - Anti-Human Antibody Blood Sample

  13. Punnet Square and Paternity Testing Genotype: alleles (AA, AO, BB, BO, AB, OO) Phenotype: expression (A, B, O)

  14. Nature of Blood • The word blood refers to a highly complex mixture of cells, enzymes, proteins, and inorganic substances. • Plasma, which is the fluid portion of blood, is composed principally of water. • Red blood cells (erythrocytes), white blood cells (leukocytes), and platelets are the solid materials suspended in plasma. • Antigens, usually proteins, are located on the surface of red blood cells and are responsible for blood-type characteristics. FORENSIC SEROLOGY

  15. Blood Typing • More than 15 blood antigen systems have been identified, but the A-B-O and Rh systems are the most important. • An individual that is type A has A antigens on his/her red blood cells, type B has B antigens, AB has both A and B antigens, and type O has neither A nor B antigens. • Rh factor is determined by the presence of another antigen, the D antigen. • People having the D antigen are Rh positive; those not having the antigen are Rh negative. • For every antigen there is a specific antibody that will react with it to form clumps known as agglutination. • Thus, if serum containing anti-B is added to red blood cells carrying B antigen, they will immediately react. FORENSIC SEROLOGY

  16. Serology • The term serology is used to describe a broad scope of laboratory tests that use specific antigen and serum antibody reactions. • The identity of each of the four A-B-O blood groups can be established by testing the blood with anti-A and anti-B sera. • The concept of specific antigen-antibody reactions has been applied to immunoassay techniques for the detection of drugs of abuse in blood and urine. FORENSIC SEROLOGY

  17. Immunoassay • A number of immunological assay techniques are commercially available for detecting drugs through antigen-antibody reaction. • One such technique, the enzyme-multiplied immunoassay technique (EMIT), is used by toxicologists because of its speed and high sensitivity for detecting drugs in urine. • In a typical EMIT analysis, antibodies that will bind to a specific drug are added to the subject’s urine. • Other immunoassay procedures are also available, such as radioimmunoassay (RIA) which uses drugs labeled with radioactive tags. FORENSIC SEROLOGY

  18. Antigen-Antibody Reaction • When an animal, such as a rabbit or mouse, is injected with an antigen its body will produce a series of different antibodies, all of which are designed to attack some particular site on the antigen of interest. • This collection of antibodies is known as polyclonal antibodies. • Alternately, a more uniform and specific collection of antibodies designed to combine with a single antigen site can be manufactured. • Such antibodies are known as monoclonals. FORENSIC SEROLOGY

  19. Forensics of Blood • The criminalist must be prepared to answer the following questions when examining dried blood: • (1) Is it blood? • (2) From what species did the blood originate? • (3) If the blood is of human origin, how closely can it be associated to a particular individual? • The determination of blood is best made by means of a preliminary color test. FORENSIC SEROLOGY

  20. The Tests • A positive result from the Kastle-Meyer color test is highly indicative of blood. • Hemoglobin causes a deep pink color. • Alternatively, the luminol test is used to search out trace amounts of blood located at crime scenes. • Produces light (luminescence) in a darkened area. • Microcrystalline tests, such as the Takayama and Teichmann tests, depend on the addition of specific chemicals to the blood so that characteristic crystals will be formed. FORENSIC SEROLOGY

  21. The Tests • Once the stain has been characterized as blood, the precipitin test will determine whether the stain is of human or animal origin. • The precipitin test uses antisera normally derived from rabbits that have been injected with the blood of a known animal to determine the species origin of a questioned bloodstain. • Once it has been determined that the bloodstain is of human origin, an effort must be made to associate or dissociate the stain with a particular individual. FORENSIC SEROLOGY

  22. A-B-O vs DNA • Prior to the advent of DNA typing, bloodstains were linked to a source by A-B-O typing and the characterization of polymorphic blood enzymes and proteins. • This approach has now been supplanted by the newer DNA technology. • DNA analysis has allowed forensic scientists to associate blood and semen stains to a single individual. FORENSIC SEROLOGY

  23. Stain Patterns of Blood • The crime scene investigator must remember that the location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the events that produced the bleeding. • Surface texture and the stain’s shape, size, and location must be considered when determining the direction, dropping distance, and angle of impact of a bloodstain. FORENSIC SEROLOGY

  24. Stain Patterns of Blood • Surface texture is of paramount importance. In general, the harder and less porous the surface, the less spatter results. • The direction of travel of blood striking an object may be discerned because the pointed end of a bloodstain always faces its direction of travel. • The impact angle of blood on a flat surface can be determined by measuring the degree of circular distortion. At right angles the blood drop is circular, as the angle decreases, the stain becomes elongated. • The origin of a blood spatter in a two-dimensional configuration can be established by drawing straight lines through the long axis of several individual bloodstains. The intersection or point of convergence of the lines represents the origin point. FORENSIC SEROLOGY

  25. Heredity and Paternity • The transmission of hereditary material is accomplished by means of microscopic units called genes, located on chromosomes. • Alternative forms of genes that influence a given characteristic (such as eye color or blood type) are known as alleles. • Paternity testing has historically involved the A-B-O blood typing system, along with blood factors other than A-B-O. • Currently, paternity testing has implemented DNA test procedures that can raise the odds of establishing paternity beyond 99 percent. FORENSIC SEROLOGY

  26. Testing for Seminal Stains • Many of the cases sent to a forensic laboratory involve sexual offenses, making it necessary to examine exhibits for the presence of seminal stains. • The best way to locate and at the same time characterize a seminal stain is to perform the acid phosphatase (an enzyme secreted into seminal fluid) color test. • A purple color indicates acid phosphatase enzyme. • Semen can be unequivocally identified by either the presence of spermatozoa or of p30, a protein unique to seminal plasma. • Forensic scientists can successfully link seminal material to an individual by DNA typing. FORENSIC SEROLOGY

  27. Rape Evidence • The rape victim must undergo a medical examination as soon as possible after the assault. • At that time the appropriate items of physical evidence including clothing, hairs, and vaginal and rectal swabs can be collected for subsequent laboratory examination. • All outer and undergarments should be carefully removed and packaged separately in paper (not plastic) bags. • Bedding, or the object upon which the assault took place, may also be carefully collected. FORENSIC SEROLOGY

  28. Rape Evidence • If a suspect is apprehended within 24 hours of the assault, it may be possible to detect the victim’s DNA on the male’s underwear or on a penile swab of the suspect. • Items routinely collected from the suspect include all clothing, pubic hair, head hair, penile swab, and a blood sample or buccal swab for DNA typing. • The forceful physical contact between victim and assailant may result in a transfer of such physical evidence of blood, semen, saliva, hairs, and fibers. FORENSIC SEROLOGY

More Related