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Forensic Serology.
Blood Classification

Blood factors are controlled genetically

>100 known blood factors
More than 15 classification systems e.g.
A-B-O system.

What is blood?
1. Plasma
– fluid portion, mainly water.
2. Cells
- red blood cells (erythrocytes)
- white blood cells (leukocytes)
- platelets
(Note: serum is the yellowish fluid after blood clots.)
What about blood types?

Antigens : impart the blood type
characteristics on RBC’s.
A-B-O system: presence or absence of A or
B antigens.
 Rh system: presence or absence of D
antigen.


Antibodies: proteins found in the serum.

Antibodies have two reactive sites allowing
them to attach to two of the same antigens
simultaneously  agglutination
Antibodies and Antigens in whole
blood.
Blood type
A
Antigens on
RBC
A
Antibodies in
Serum
Anti-B
B
B
Anti-A
AB
A, B
O
Neither anti-A
nor anti-B
Neither A nor B Both anti-A and
anti-B
What is Serology?
Any test involving antibody-antigen reactions
e.g. A-B-O agglutination reaction, many
immunoassay techniques.
Immunoassay Techniques.

Antibody-antigen reactions used to detect
drugs in urine and blood.
- EMIT tests such as THC kits, methadone
test kits.

Antibodies capable of reacting with the
drugs are produced in animals.
Making antibodies for ELISA
drug determination.
Characterization of Blood
1. Is it blood?
2. What species?
3. If human, can it be associated with a
particular individual?
Hemoglobin
Preliminary Tests
1. Is it blood?



Benzidine color test or Kastle-Meyer color test.
Luminol test
Microcrystalline tests
2. What species?

Precipitin test
Antibody-Antigen precipitation
reaction.
Individualizing blood evidence.
Blood is class evidence! ….further testing may
“individualize” this evidence to one person.
Polymorphic Proteins
 Enzymes (proteins) that exist in different forms.

Enzymes separated into individual components
called isoenzymes, each having the same (or
similar) enzyme activity.
Phosphoglucomutase (PGM)

Common Isoenzymes of PGM
PGM 1 (58%), PGM 2-1 (36%), PGM 2 (6%).
Variation within the population helps decrease the
number of “likely suspects”.
Bloodstain Patterns.
Must consider:
 Surface Texture
 Direction of Travel
 Impact angle of blood
 Origin of spatter.
Surface Texture
Surface texture can change the appearance of the spatter and
must be taken into consideration.
Smooth hard
surface
Wood or
concrete
Direction of Travel
Point of Convergence
By drawing a line through the long axis of a group of
bloodstains and determining where they cross each other
the point of convergence can be determined.
Convergence to determine point of
origin.
Point of Origin

Construction of a 3-D model
Angle of Impact

By measuring the length and width of the blood stain, the
angle and direction of impact can be determined.
sin A = width of bloodstain
length of bloodstain
Velocity of Impact
Low
 Medium
 High

Low Velocity


- free falling drops of blood.
- sometimes called “passive” spatter.
Medium Velocity

Produced when one object strikes another

- blunt (fist,club) or sharp (knife) trauma.
High Velocity
- gunshot, power tools, explosion.

Impact Spatter
Back and forward spatter
(arrow shows direction of
projectile)

Arterial spurt pattern.
Detection By Luminol
Transfer print detected using
luminol
Heredity: it’s in the genes!

Gene is the basic unit of hereditary.

Genes are positioned on chromosomes.
- 46 chromosomes (23 pairs)
“Sex chromosomes”: X and Y
XX
female
XY
male
Origin of different characteristics

Genes that influence a given characteristic
(PHENOTYPE) are grouped together in allelles.

Every characteristic requires a pair of genes (two
genes). This is the GENOTYPE.
both the same - homozygous
different
- heterozygous
Paternity Testing

Disputed paternity can be resolved by
determining blood type.
Punnet Square:
A
B
A
AA
AB
A
AA
AB