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% of blood content) l l The other 45% is solid material – –Red and white cells and platelets

Blood Cells l l 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 l l White blood cells (WBC’s) – –Part of the immune system – –Contains a nucleus – –Also called leukocytes l l Platelets – –Used for forming clots. Serum is the liquid that separates out. Contains antibodies

Searching for Blood l l 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)

Searching for Blood l l 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.

Searching for Blood l l Hemastick – –Designed to test for blood in urine (dipstick) – –Positive result = green!

Human or non-human? l l 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.

Precipitin Test l l The human antibodies are collected from the rabbit serum. l l A sample of unknown blood is combined with the new antibodies. l l If a precipitate forms then the antibody matches the antigen on the blood. l l If a precipitate does NOT form then they don not match.

Human or Non-Human l l Gel Diffusion- Same idea as the precipitin test, only it is done in a container such as a petri dish. l l The gel is porous so the antibody and antigen and travel toward each other l l If a band forms, then there is a positive result. l l Electrophoresis Method (Similar method as above but uses electricity to move the antibody and antigen)

Blood Type l l Three types (alleles) of blood type gene – –A, B, O l l Each individual inherits one blood type gene from their mother & one from their father l l 6 possible combinations (genotypes) – –AA, BB, OO, AB, AO, and BO – –We write these using the letter I l l Genotype determines blood type

Blood Type

Rh Factor l l The positive or negative that follows your blood type. l l Identified as the D antigen l l Named after the Rhesus Monkey

Antibodies l l Anti-A (matches up with B antigens) l l Anti-B (matches up with A antigens) l l Anti-Rh l l Agglutination- Clumping caused by the matching of an antibody and antigen.

Secretors vs. Nonsecretors l l Secretors have A and B antigens in non- blood fluid – –80% of population l l Nonsecretors don’t have blood type antigens in saliva, semen, etc. – –Remaining 20% of population