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FORENSIC SCIENCE
Serology
1
Blood Characteristics
• Plasma--fluid portion of the blood (55%)
• Cells (45%)
– Erythrocytes--red blood cells; responsible for oxygen
distribution
– Leukocytes--white blood cells; responsible for
“cleaning” the system of foreign invaders
– Thrombocytes--platelets; responsible for blood
clotting
• Serum--liquid that separates from the blood when a clot
is formed
2
Blood Terminology
• ABO blood groups--based on having an A, B, both or
none of the factors on the red blood cell
• Rh factor--may be present on the red blood cell; positive
if present and negative if not
• Antigen--a substance found on a red blood cell
• Antibody--a substance that reacts with an antigen
• Agglutination--clumping of red blood cells; will result if
blood types with different antibodies are mixed
3
Blood Genetic Terminology
• Genotype--letters that represent different versions
(alleles) of the same gene; ex: AA, AO, BO, BB,
AB and OO
• Phenotype--words that describe the traits, physical
result of genotype; ex: A, B, O
• Heterozygous--different alleles for the same trait;
ex: AO, BO, AB
• Homozygous--the same alleles for the trait; ex:
AA, BB, OO
4
Forensic Blood Analysis
Questions to be answered:
• Is it blood?
• Is it human blood?
• Whose is it?
– Determine blood type, alcohol content, drugs present
– Determine the method(s) in which blood may have
been deposited
5
Presumptive Tests for
Blood
• Kastle-Meyer color test--a mixture of
phenolphthalein and hydrogen peroxide is tested on the
unknown liquid or dry stain
– Positive Result: the blood’s hemoglobin will cause the formation
of a deep pink color
• Leucomalachite test--leucomalachite green mixed
with acetic acid and distilled water
– Positive Result: An additional drop of sodium percblorate will turn
blood green and then darken.
• Luminol test--reaction with blood results in the
production of light
6
Human vs Animal
• Microscopic survey
• Precipitin test--blood is injected into a rabbit;
antibodies are formed; rabbit’s blood is extracted as an
antiserum; the antiserum is placed on sample blood. It will
react with human proteins. This test is very sensitive and
requires only a small amount of blood.
• Characteristic Differences
7
Animal Blood
Frog Blood
• Larger nucleic red
blood cells
8
Human Blood
• Red blood cells--5 to 6
million per mm3, no
nucleus
• White blood cells Larger but less
numerous, 5 to 10,000
per mm3
• Platelets - Tiny,
cellular fragments 350
to 500,00 per mm3
9
Blood Typing
• A blood type has antigen A and will agglutinate
with B.
• B blood type has antigen B and will agglutinate
with A.
• AB blood type has antigens A and B and will not
agglutinate with either A or B.
• O blood type has neither antigen A or B and will
agglutinate with either.
10
Blood Groups
Type
Antigen
Antibody
Can Give
Blood To:
Can Get
Blood From
A
A
B
A, AB
O, A
B
B
A
B, AB
O,B
AB
A and B
Neither
A nor B
AB
A, B, O, AB
O
Neither
A nor B
A and B
A, B, O, AB
O
Blood Reactions to Antiserum
REACTION
Anti-A Serum
Agglutination
Anti-B Serum
No agglutination
No agglutination Agglutination
Agglutination
Agglutination
No agglutination No agglutination
BLOOD TYPE
Type A
Type B
Type AB
Type O
12
Population Distribution
of Blood Types in the U. S.
Type
Percent
O
45
A
39
B
12
AB
4
13
BLOOD
PATTERN/SEROLOGICAL
RECONSTRUCTION
SCENE PATTERN
RECONSTRUCTION
LAB RESULTS
RECONSTRUCTION
1.
2.
3.
4.
5.
1.
2.
3.
4.
5.
Stain condition
Pattern
Distribution
Location
Directionality
Genetic marker typing
Age Determination
Source Determination
Race Determination
Sex Determination
From “Cracking Cases” by Dr. Henry C. Lee
14
BLOOD DROPLET
Characteristics
• A blood droplet will remain spherical in
space until it drops onto a surface
• Once a blood droplet impacts a surface, a
bloodstain is formed.
• A droplet falling from the same height,
hitting the same surface at the same angle,
will produce a stain with the same basic
15
shape.
CONDITIONS AFFECTING
BLOODSTAIN SHAPE
• Size of the droplet
• Angle of impact
• Velocity at which the blood droplet left the
original surface
• Texture of the target surface
– On clean glass or plastic--droplet will have smooth outside edges
– On a rough surface--will produce scalloping on the edges
16
Questions Answered by
Blood Spatter Interpretation
• The distance between the target surface and
the origin of blood at the time of blood shed
• The point(s) of origin of the blood
• Movement and direction of a person or an
object
• The number of blows, shots, etc. causing
the bloodshed and/or the dispersal of blood.
17
Questions Answered by
Blood Spatter Interpretation
• Type and direction of impact that produced
the bloodshed
• The position of the victim and/or object
during bloodshed
• Movement of the victim and/or object after
bloodshed
18
Bloodstain Terminology
• Angle of impact--angle at which blood strikes a
target surface.
• Bloodstain transfer--When a bloody object comes
into contact with a surface and leaves a patterned blood
image on the surface.
• Backspatter--blood that is directed back toward its
source of energy.
• Cast-off--blood that is thrown from an object in motion
19
Bloodstain Terminology
• Contact stain--general term referring to bloodstains
caused by contact between a wet, blood-bearing surface
and a second surface which may or may not have blood on
it
– Transfer--image is recognizable and may be
identifiable with a particular object
– Swipe--wet blood is transferred to a surface which did
not first have blood on it
– Wipe--a non-blood bearing object moves through a
wet bloodstain, altering the appearance of the original
20
stain
Bloodstain Terminology
• Directionality--relates to the direction a drop of blood
traveled in space from its point of origin
• Terminal velocity--the greatest speed to which a free
falling drop of blood can accelerate in air. It is dependent
upon the acceleration of gravity and the friction of the air
against the blood--approximately 25:1 feet/second.
– High velocity--greater than 100 feet per second;
gives a fine mist appearance
– Low velocity--5 feet per second or less
– Medium velocity--5 to 25 feet per second.
21
Bloodstain Pattern
• Terminal Velocity
• Directionality
• Angle of Impact
22
Blood Stain Patterns
The shape of a blood stain:


Round--if it falls straight down at a 90 degree
angle.
Elliptical--Blood droplet elongates as the angle
decreases from 90 to 0 degrees. The angle can
be determined by the following formula:
width
=
sine of the impact angle
length
23
IMPACT
• The more acute the angle of impact, the
more elongated the stain.
• 90 degree angles are perfectly round with
80 degree angles taking on a more elliptical
shape.
• At about 30 degrees the stain will begin to
produce a tail.
• The more acute the angle, the easier it is to
determine the direction of travel.
24
Blood Stains
• The harder and less porous the
surface, the less the blood drop
will break apart.
• The softer and more porous the
surface, the more a blood drop
will break apart.
• The pointed end of the blood
stain faces the direction the stain
is traveling.
25
Area of Intersection
The location of the blood
source can be determined
by drawing lines the
various blood droplets to
the point where they
intersect. This is the
blood’s origin.
26
Area of Convergence
The area of convergence
is the point of origin;
the spot where the
“blow” occurred.
It is determined by
drawing a line from the
area of intersection
straight up to where to
where the angle of impact
would intersect
27
CRIME SCENE
What evidence
can you see in
this crime
scene? What
story does the
scene tell?
28
Bring In The Dogs!
The dog locates
human scent. A
closer look
shows that the
ashes have
human remains
and clothing.
In addition,
look closely at
the rocks on the
next slide.
29
Blood Evidence
• Class evidence for blood would include blood
type. If you can determine the DNA you would
have individual evidence.
• Blood stain patterns are considered circumstantial
evidence in a court room. Experts could argue
many points including direction of stains, height
of the perpetrator, position of the victim, left/right
hand, whether the body was moved, etc.
31
Sperm
• Among the smallest and most
highly specialized cells in the
human body.
• Has a head and a tail
• Contains 23 chromosomes with
the genetic material found in the
head
• Males release 2.5 to 6 milliliters
of seminal fluid per ejaculation
with approximately 100 million
sperm per milliliter.
Magnified 400X
32
Semen
Determination of Seminal Fluid
• Acid phosphatase color test
– the presence of acid phosphatase, the enzyme
secreted by the prostate gland into the seminal
fluid, will turn purple when sodium alpha
naphthylphosphate and Fast Blue B solution are
placed on it.
– It will also fluoresce under UV light when it
comes in contact with 4-methyl umbelliferyl
33
phosphate.
Semen (cont.)
Determination of Seminal Fluid
• Prostate Specific Antigen (PSA) or p30--unique to
seminal plasma
– P30 is isolated and injected into a rabbit where
antibodies are produced (anti-p30)
– The stain extract is place in one well of an
electrophoresis plate and the anti-p30 in the opposite
well. The electric is applied and the antigens and
antibodies move toward each other. The formation of a
precipitation line between the wells shows the presence
of p30 in the sample stain. It must be seminal fluid. 34
Secretors
• 80% of people are considered secretors. Their
blood-type antigens are found in high
concentration in their body fluids such as
saliva, semen, vaginal secretions and gastric
juice. If you are a secretor, you will have a
higher concentration of A and B antigens than
does your blood!!
• With the advent of DNA, the secretor evidence
is not as important as it once was.
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