Forensic Serology Ch. 12. Blood Baby...cute. Nature of Blood. The word ‘blood’ refers to a highly complex mixture of cells, enzymes, proteins, and inorganic substances. http://www.youtube.com/watch?v=qX7Fd_QNXYs. Karl Landsteiner. 1901 A, B, O system of blood classification
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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.
Rh factor is determined by the presence of another antigen, the D antigen.
For every antigen there is a specific antibody that will react with it to form clumps known as agglutination.
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.
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 the EMIT assay, a drug that may be present in a urine specimen will compete with added labeled drug for a limited number of antibody binding sites. The labeled drugs are indicated by an asterisk. Once the competition for antibody sites is completed, the number of remaining unbound labeled drug is proportional to the drug’s concentration in urine.
Alternately, a more uniform and specific collection of antibodies designed to combine with a single antigen site can be manufactured; monoclonals.
The criminalist answers the following questions when examining dried blood:
The determination of blood is best made by means of a preliminary color test.
Blood at the crime scene can be in the form of pools, drops, smears, or crusts.
Drops of blood tell the height and angle from which the blood fell. The forensic science of blood spatter analysis says that blood which fell perpendicular to the floor from a distance of 0-2 feet would make a circular drop with slightly frayed edges.
Drops from a higher distance would have more pronounced tendrils fraying off the edges (a sunburst pattern).
A blood smear on the wall or floor tells the direction of force of the blow.
Refrigerated red blood cells have a shelf life of about 42 days, and the serum containing white blood cells can be refrigerated up to a year.
as per the following steps:
1. Blood samples are collected from the victim, defendant, and crime scene2. White blood cells are separated from red blood cells3. DNA is extracted from the nuclei of white blood cells
4. A restrictive enzyme is used to cut fragments of the DNA 5. DNA fragments are put into a bed of gel with electrodes 6. Electric current sorts DNA fragments by length7. An absorbent blotter soaks up the imprint; radioactively treated, and an X-ray photograph (called an autoradiograph)
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.
The direction of travel of blood striking an object may be determined 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-dimensions can be established by drawing straight lines through the long axis of several bloodstains.
Illustration of stain convergence on a two-dimensional plane. Convergence represents the point from which the stains emanated. Courtesy Judith Bunker, J. L. Bunker & Assoc., Ocoee, FL
Length (c) 3.0cm
SIN < = 0.5
< = 30 degrees
A-B-O blood typing system, along with blood factors other than A-B-O. Elimination or inclusion.
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.
successfully link seminal
material to an individual by
An antibody–antigen–antibody sandwich or complex is seen as a colored band. This signifies the presence of PSA in the extract of a stain and positively identifies human semen.
All outer and undergarments should be carefully removed and packaged separately in paper (not plastic) bags.