Chapter 12 Forensic Serology. Forensic Serology Introduction. 1901, Karl Landsteiner found blood to be distinguishable by group Led to the classification of the ABO system By 1937, the Rh factor was demonstrated Numerous other blood factors/groups discovered
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Forensic Serology Introduction • 1901, Karl Landsteiner found blood to be distinguishable by group • Led to the classification of the ABO system • By 1937, the Rh factor was demonstrated • Numerous other blood factors/groups discovered • More than 100 different blood factors known to exist • Total of 30 different blood groups recognized by International Society of Blood Transfusion
Forensic Serology Introduction • For the most part, no two individuals have the same combination of blood factors • Blood factors are controlled by genetics; therefore, they are highly distinctive • DNA has become the favored method of identifying individual through blood
The Nature of BloodAntigens and Antibodies • Blood is a complex mixture of cells, enzymes, proteins, and inorganic substances • Plasma – the fluid portion composed mostly of water and makes up 55% of blood content • Cells - red blood cells (erythrocytes), white blood cells, & platelets are suspended in plasma and accounts for 45% of blood content • Blood clots occur when a protein, fibrin, traps RBCs; the liquid that separates from blood when a clot is formed is the blood serum
Antigens and Antibodies • Red Blood Cells • Transport oxygen from lungs to body tissue and then carbon dioxide from tissue to lungs • Antigens are present on the surface of the RBCs • Antigens impart blood-type characteristics to the red blood cells
Antigens • A type A individual has A antigens on the surface the of the RBCs • A type B individual has B antigens on the surface the of the RBCs • A type AB individual has bothA and B antigens on the surface the of the RBCs • A type O individual has neitherA or antigens on the surface the of the RBCs
Antigens • Another blood factor, RH factor or D factor, has been found • A person with the D antigen is Rh positive; a person without the D antigen is Rh negative
Antigens and Antibodies It is the presence or absence of the three antigens – A, B, or D – that determine the compatibility of a blood donor and recipient. The fundamental principle of blood typing is that for every antigen, there exists a specific antibody.
Antibodies • Antibody – a protein that destroys or inactivates a specific antigen; antibodies are found in the blood serum • The blood serum which contain antibodies is antiserum • For every antigen, there is a specific antibody • Anti-A is the antibody specific to antigen A • Anti-B is the antibody specific to antigen B • Anti-D is the antibody specific to antigen D
Agglutination • An antibody will react only with its specific antigen • If serum containing anti-B is added to RBCs carrying the B antigen, the two will combine • Antibodies are typically bivalent – they have two reaction sites and can attach to two antigens on different RBCs • The clumping together of RBCs by the attachment of antibodies is called agglutination
Blood Typing • Serology refers to a broad scope of laboratory tests that use specific antigen and serum antibodies reactions Blood typing • Test blood with anti-A and anti-B serum • Test for the presence of antibodies, anti-A or anti-B, with known antigens
If your blood type is . . . Out of 100 donors . . . . .
Forensic Blood Test • Forensic Scientist must answer the following questions when examining dried blood: • Is it blood? • From what species did the blood originate? • If the blood is human, how closely can it be associated with a particular individual?
Color Tests Luminol Precipitin Gel Diffusion Iso-enzymes Forensic Blood Tests
Color Tests • Phenolphthalein indicator (Kastle-Meyer color test) • When mixed with blood and hydrogen perioxide, the hemoglobin will turn pink
Luminol Test • When in contact with blood, produces light • Highly sensitive – can detect bloodstains diluted up to 300,000 times • Used to spray large areas such as carpets, walls, flooring, or interior of a vehicle • Will not interfere with DNA testing
Precipitin • Used to determine if blood is of human origin • Animals will produce antibodies when injected with human blood; these antibodies, called human serum, can be isolated
Precipitin (p. 338) • Layer a sample of the bloodstain in a small test tube with a layer of human antiserum on top. The human blood will react with the antiserum forming a cloudy band in the test tube.
Precipitin (p. 339) 2. Gel diffusion Extracted bloodstains and human anti-serum are placed in separate openings on opposite sides of a gel. Antigens and antibodies induced to move towards each other when an electrical charge is applied. A specific line is formed if the antigen and antibodies react together.
Precipitin • Very sensitive tests requiring a small amount of blood • Human bloodstains can be dried for as long as 10 to 15 years • Diluted bloodstains can also give positive results
Iso-enzymes • Forensic scientists can study polymorphic enzymes – enzymes that exist in different forms • These enzymes are iso-enzymes • Multiple forms of an enzyme each with a similar function • Iso-enzymes can be separated by gel electrophoresis; different people will have different iso-enzymes which can provide individual characteristics to the blood stain
The location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the events that must have occurred to have produced the bleeding. • The significance of the position and shape of blood patterns with respect to their origin and trajectory is exceedingly complex and requires an experienced examiner • An analysis usually requires controlled experiments creating an environment comparable to the crime scene.
Stain Patterns of Blood Herbert L. MacDonell’s observation’s: • Surface texture is important in the interpretation of blood stain patterns and correlations betweren standards and unknowns are valid only if identical surfaces are used. In general, the harder and less porous the surface, the less splatter results.
Stain Patterns of Blood • The direction of travel of blood striking an object may be discerned by the stain’s shape. The pointed end of a bloodstain always faces its direction of travel.
Stain Patterns of Blood 3. It is possible to determine the impact angle of blood on a flat surface by measuring the degree of circular distortion of the stain. A drop of blood striking a surface at right angles gives rise to a nearly circular stain; as the angle decreased, the stain becomes elongated in shape.
Stain Patterns of Blood 4. 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 area of convergence of the lines represents the area from which the blood emanated.
Stain Patterns of Blood Resources • http://projects.nfstc.org/gallery/main.php?g2_itemId=3857 • http://www.crimescene-forensics.com/Blood_Stains.html • http://www.videojug.com/interview/csi-and-blood-evidence-2#why-are-blood-stains-studied-in-csi