forensic serology. blood l l a complex mixture of cells, enzymes, proteins & inorganic...
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![Page 1: Forensic Serology. Blood l l A complex mixture of cells, enzymes, proteins & inorganic substances l l Fluid portion of blood is called the plasma (55%](https://reader035.vdocuments.us/reader035/viewer/2022062518/56649f065503460f94c1b99d/html5/thumbnails/1.jpg)
Forensic SerologyForensic Serology
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Blood
A complex mixture of cells, enzymes, proteins & inorganic substances
Fluid portion of blood is called the plasma (55% of blood content)
The other 45% is solid material
– Red and white cells and platelets
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Blood Cells Red blood cells (RBC’s)
– Transports oxygen using the protein hemoglobin– Surface of the cells contain antigens (proteins used for cell identification)– Contains no nucleus– Also called erythrocytes
White blood cells (WBC’s)– Part of the immune system– Contains a nucleus– Also called leukocytes
Platelets – Used for forming clots. Serum is the liquid that separates out. Contains antibodies
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Searching for Blood
Kastle-Meyer– Reacts with hemoglobin in the blood. Uses
phenolphthalein and hydrogen peroxide. Turns a deep pink color.
– Can produce false positives (vegetables such as horseradish and potato)
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Searching for Blood
Luminol– Also reacts with hemoglobin in the blood.
– A positive reacts produces a glow when under a blacklight.
– Very sensitive- Can detect stains that have been diluted up to 300,000 times.
– Used for very large areas, such as walls, floors, interiors of cars.
– Will not interfere with further DNA testing.
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Searching for Blood
Hemastick– Designed to test for blood in urine (dipstick)– Positive result = green!
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Human or non-human?
Precipitin Test- Looking for antibodies to react with blood– Human antibodies can be created in the blood
serum of rabbits– Antibodies are naturally created when a foreign
substance/cell is encountered. This is how your body protects itself from future attacks.
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Precipitin Test
The human antibodies are collected from the rabbit serum.
A sample of unknown blood is combined with the new antibodies.
If a precipitate forms then the antibody matches the antigen on the blood.
If a precipitate does NOT form then they don not match.
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Human or Non-Human
Gel Diffusion- Same idea as the precipitin test, only it is done in a container such as a petri dish.
The gel is porous so the antibody and antigen and travel toward each other
If a band forms, then there is a positive result.
Electrophoresis Method (Similar method as above but uses electricity to move the antibody and antigen)
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Blood Type
Three types (alleles) of blood type gene– A, B, O
Each individual inherits one blood type gene from their mother & one from their father
6 possible combinations (genotypes)– AA, BB, OO, AB, AO, and BO
– We write these using the letter I
Genotype determines blood type
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Blood Type
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Rh Factor
The positive or negative that follows your blood type.
Identified as the D antigen Named after the Rhesus Monkey
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Antibodies
Anti-A (matches up with B antigens) Anti-B (matches up with A antigens) Anti-Rh
Agglutination- Clumping caused by the matching of an antibody and antigen.
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Secretors vs. Nonsecretors
Secretors have A and B antigens in non-blood fluid– 80% of population
Nonsecretors don’t have blood type antigens in saliva, semen, etc.– Remaining 20% of population