Forensic SerologyForensic Serology

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

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

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)

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.

Searching for Blood

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

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.

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.

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)

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

Blood Type

Rh Factor

The positive or negative that follows your blood type.

Identified as the D antigen Named after the Rhesus Monkey

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.

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