Transcript Serology PPT

Chapter 8
Serology
“Out damned spot! Out, I say
Here’s the smell of the blood still,
All the perfumed of Arabia will not
Sweeten this little hand. Oh, Oh, Oh!”
—William Shakespeare’s Lady Macbeth, in Macbeth
http://noppa5.pc.helsinki.fi/koe/corr/cor7.html
Correlation coefficient
Learning Objectives
Students should be able to :
 List the A-B-O antigens and
antibodies found in the
blood for each of the four
blood types: A, B, AB and
O.
 Understand and describe
how whole blood is typed.
 List and describe forensic
tests used to characterize
a stain as blood.
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Learning Objectives
Students should be able to :
 List and describe
forensic tests used to
characterize a stain as
blood.
 Understand the concept
of antigen-antibody
interactions and how it
is applied to species
identification and drug
identification.
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Learning Objectives
Students should be able to :
 Contrast chromosomes
and genes.
 Use the Punnett square
to determine the
genotypes and
phenotypes of offspring.
Father’s genotype
O
O
Mother’s
genotype
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A
B
3
Learning Objectives
Students should be able to :
 List the laboratory tests
necessary to
characterize seminal
stains.
 Explain how suspect
blood and semen stains
are properly preserved
for laboratory
examination.
UV light makes seminal fluids glow brightly
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Learning Objectives
Students should be able to :
 Describe the proper collection of physical
evidence in a rape investigation.
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Forensic Serology
 Forensic serology is the study of blood, saliva,
semen or sweat in manners pertaining to the law.
 From 1950 to the early 1990s, forensic serology
was a most important part of lab procedures.
 With the development of DNA techniques, more time,
money, and significance was placed in developing DNA
labs.
 However, with limited funds and the time required for
DNA testing, many labs still use many of the basic
serology testing procedures.
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Historical Perspective
of Blood Typing
In 1901, Karl Landsteiner discovered that there are four
different types of human blood based on the presence or
absence of specific antigens found on the surface of the
red blood cells.
By 1937, Landsteiner and Weiner reported the discovery
of the Rh factor by studying the blood of the Rhesus
monkey. 85% of Caucasians, 94% of Black Americans
and 99% of all Asians are Rh positive.
More than 100 different blood factors have been
identified.
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I. The Nature of Blood
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Blood Characteristics




Chapter 8
Plasma is the fluid portion of the blood
(55%)
Cells (45%)
 Erythrocytes are red blood cells.
They are responsible for oxygen
distribution.
 Leukocytes are the white blood
cells; they are responsible for
“cleaning” the system of foreign
invaders.
 Thrombocytes or platelets are
responsible for blood clotting
Serum is the liquid that separates from
the blood when a clot is formed.
Antigens, usually proteins, are located
on the surface of RBCs and are
responsible for blood-type
characteristics.
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Human Blood
 Red blood cells are most
numerous; 5 to 6 million
per mm3
 White blood cells are
larger and less numerous;
5000 to 10,000 per mm3
 Platelets are tiny, cellular
fragments; 350,000 to
500,00 per mm3
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Blood Terminology
 ABO blood groups—based on having an A, B, both or no
antigens on red blood cells
 Rh factor—may be present on red blood cells; positive if
present and negative if not
 *Antigen—a substance that can stimulate the body to make
antibodies. Certain antigens (usually proteins) located on the
red blood cell’s membrane account for blood type.
 *Antibody—a substance that reacts with an antigen
 Agglutination—clumping of red blood cells; will result if blood
types with different antigens are mixed
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Blood Typing
 More than 15 blood antigen systems
have been identified, but the 2 most
important are :
 the A-B-O system
 A, B, AB and O blood types
 the Rh system
 Rh positive and Rh negative
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Blood Typing
 The identity of each of the four A-B-O
blood groups can be established by
testing the blood with anti-A and anti-B
sera.
 For every antigen there is a specific
antibody that will react with it to form
clumps known as agglutination.
 If serum containing anti-B is added to RBCs
carrying the B antigen, they will immediately react
(clump together).
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Blood Typing (A-B-O)
 Blood type A has antigen A on the surface of
the cell and will agglutinate with blood type B.
 Blood type B has antigen B on the surface of
the cell and will agglutinate with blood type A.
 Blood type AB has antigens A and B on the
surface of the cells and will not agglutinate with
either type A or B blood.
 Blood type O has neither antigen A nor B and
will not agglutinate.
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Antigen and Antibody
Antigens are large
molecules (usually
proteins) on the surface
of cells, viruses, fungi,
bacteria, and some nonliving substances such
as toxins, chemicals,
drugs, and foreign
particles. The immune
system recognizes
antigens and produces
antibodies that destroy
substances containing
antigens.
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BLOOD TYPES
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Blood Typing Animation
Click here for animation and mini quiz
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ABO Blood System
(Antigen)
Anti-B
Chapter 8
Anti-A
none
Anti-A and Anti-B
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http://gslc.genetics.utah.edu/units/basics/blood/types.cfm
Blood Typing and Cross-Reactions
Recipient
blood
type
B
is ____
Chapter 8
Donor blood
A
type is ____
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Blood Typing
Click for
Blood
typing
simulation
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Go to the following web site to
play the blood typing game
 First Go to “How to play the game”
 http://nobelprize.org/educational_g
ames/medicine/landsteiner/
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ABO Blood Types
 Based on the presence (or absence) of antigen(s) on the red blood cell
membrane
 There are 2 types of antigens that can be present,
or
A
B.
A person can inherit one, both or none
A (A antigen)
B (B antigen)
AB (both A + B antigen) O (no antigens)
About 2 – 8 months after birth, you develop antibodies to the blood types
you do not have.
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Blood Transfusion
A person who is blood type A will have the ____
A antigen on their
RBC surface.
B antibodies.
In their plasma, they will have anti- _____
B antigen on their
A person who is blood type B will have the ____
RBC surface.
A antibodies.
In their plasma, they will have anti- _____
What will happen if a person with blood type B donates
blood to a person with blood type A?
The B antibodies of the A plasma will attack and destroy the B
red blood cells, causing dangerous and often fatal blood clotting.
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Blood Groups
Type
Antigen
(on RBC)
Antibody
(in serum)
Can Give
Blood To
Can Get
Blood From
A
A
Anti-B
A, AB
O, A
B
B
Anti-A
B, AB
O,B
AB
A and B
Neither
Anti-A nor
Anti-B
AB
A, B, O, AB
O
Neither
A nor B
Anti-A and
Anti-B
A, B, O, AB
O
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Population Distribution
of Blood Types in the U.S.
Type
Chapter 8
Percent
O
43
A
42
B
12
AB
3
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Blood Typing (Rh factor)
 Rh factor is determined by the
presence of the D antigen.
 Rh positive people have the D antigen
 Rh negative people lack the D antigen
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Secretors
80% of the population are secretors.
Their blood-type antigens are found in
high concentration in their body fluids
such as: saliva
semen
vaginal secretions
gastric juice
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Please Do Now
Please write at least
5 lines to explain this
cartoon in your
composition book.
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What is one thing you can give
and still keep?
•
•
•
•
•
•
•
Chapter 8
Your word
Hope
Fingeprints
Blood
Name
Life (pregnancy)
Knowledge
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Learning Objectives
Students should be able to :
 List and describe
forensic tests used to
characterize a stain as
blood.
 Understand the concept
of antigen-antibody
interactions and how it
is applied to species
identification and drug
identification.
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II. Immunoassay Techniques
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Serology
 Describes a broad scope of laboratory tests
that use specific antigen and serum
antibody reactions.
 The concept of specific antigen-antibody
reactions has been applied to immunoassay
techniques for the detection of drugs of
abuse in blood and urine.
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Immunoassay
 The concept of antigen-antibody reaction is used in
 blood typing
 the detecting of drugs in blood and urine
 Thousands of individuals are subjected to urinalysis
tests for the presence of drug-abuse. Such as:
Military personnel
Transportation industry employees
Police and correction personnel
Pre-employment drug screenings
 Note: Antibodies that react with drugs do NOT
exist naturally but can be produced in animals such
as rabbits.
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Testing Urine for Drugs
One-step immunoassay for detection
of drug abuse in urine
Read Supreme Court Ruling
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Immunoassay
 A number of immunological assay techniques
are commercially available for detecting drugs
through antigen-antibody reaction.
 Radioimmunoassay (RIA) uses drugs labeled
with radioactive tags.
 Enzyme-multiplied immunoassay technique
(EMIT) is uses an enzyme tag for detecting
drugs in urine.
 Immunoassay is ONLY presumptive in nature
and its result must be confirmed by additional
testing. (not totally specific for any drug)
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Radioimmunoassay (RIA)
see p. 273 Fig. 8 - 3
uses drugs labeled with radioactive tags.
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Enzyme-Multiplied Immunoassay
Technique (EMIT) see p. 274
used for detecting drugs in urine and fingernails
The method of screening for drug use in a fingernail test
is the five panel, Enzyme Multiple Immunoassay Test
(EMIT).
Five drugs are tested for with the qualitative detection of
cocaine, amphetamines / methamphetamines (ecstasy),
opiates (heroin, morphine),PCP (angels dust,hog) and
tetrahydrocannabinol (marijuana, hashish) drug testing
in urine.
Results of a fingernail sample will represent drug use
that is approximately 4-6 months from the time of
ingestion. Fingernails can be clipped, or, if length does
not allow, can be shaved in a safe and pain-free sample
collection.
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Immunoassay

Enzyme-multiplied immunoassay technique
(EMIT) is used by toxicologists because of its
1.
2.

speed for detecting drugs in urine and
high sensitivity for detecting drugs in urine.
In a typical EMIT analysis, antibodies that will
bind to a specific drug are added to the subject’s
urine.
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Antigen-Antibody Reaction
(polyclonal antibodies)
 When an animal, such as a rabbit or mouse,
is injected with an antigen its body will
produce a series of different antibodies, all
of which are designed to attack some
particular site on the antigen of interest.
 This collection of antibodies is known as
polyclonal antibodies.
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Antigen-Antibody Reaction
(monoclonal antibodies)
see p. 275
 A more uniform and specific collection of
antibodies designed to combine with a
single antigen site can be manufactured.
 Such antibodies are known as monoclonals.
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III. Forensic Characterization
of Bloodstains
IS IT BLOOD?
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Unknown Stain at a Scene
3 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
The determination of blood is best made by means of
a preliminary color test.
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Presumptive (Color) Tests
for Blood Determination
 Kastle-Meyer color test—a mixture of
phenolphthalein and hydrogen peroxide; the
hemoglobin will cause the formation of a deep pink
color if blood is present
 Hematest® tablet—reacts with the heme group in
blood causing a green color
 Luminol test—reaction with blood to produce light
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Color Tests for Blood
(Kastle - Meyer Tests)
 Replaced benzidine color test (after being identified
as a carcinogen)
 a mixture of phenolphthalein and hydrogen
peroxide;
 the hemoglobin will cause the formation of a deep
pink color if “blood” is present
 Not specific for blood - *false positive given by:
 Potatoes
 horseradish
* Neither probably not encountered in criminal situations
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Color Tests for Blood
(Hemastix strips or Hematest® tablets)
 reacts with the heme group in blood
causing a green color
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Presumptive (Color) Tests for
Blood Determination (Luminol)
 Reaction with blood to produce light
 Spray luminol on object
 Darken room
 Bloodstains react to produce a blue glow (luminescence)
 Used to check large areas
 Extremely sensitive
300,000 times
 Can detect bloodstains diluted up to ____________
 Does NOT interfere with subsequent DNA testing
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Microcrystalline Tests
 Depend on the addition of specific
chemicals to the blood so that characteristic
crystals will be formed
 ID of blood is made more specific if
microcrystalline tests are done
 Less sensitive than color tests
 More susceptible to interference from
contaminants present in the stain
 Two most popular tests are:
 Takayama test and Teichmann test
Click to view Takayama crystals
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Precipitin Test
(human vs. animal blood)
see p. 279 Fig. 8 - 5
 Determines whether the stain is of
human or animal origin
 Uses antisera normally derived from
rabbits that have been injected with
the blood of a known animal to
determine the species origin of a
questioned bloodstain.
 If human blood, then determine whose
blood
is
it.
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Chapter 8
Precipitin Test
see p. 279 Fig. 8 - 5
 blood is injected into a rabbit;
 antibodies are formed;
 the rabbit’s blood is extracted as an
antiserum;
 the antiserum is placed on sample blood.
 The sample will react with human proteins, if
human blood is present.
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Precipitin Test
Why is this a good test for determining if it
human blood?
 very sensitive
 requires only a small amount of blood
 Blood can be old and still give a positive result
 Bloodstains from 4000-5000 year old mummies have given
positive results
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Gel Diffusion
 antibodies and
antigens
diffuse or
move towards
one another on
an agar plate.
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Human vs Animal Blood
Microscopic observation
Frog Blood
Human Blood
Larger nucleic red
blood cells
nonnucleated red
blood cells
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IV. Bloodstain Patterns
Science of Murder: Blood Spatter Video
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More about Serology
For additional information about blood
evidence, and famous crimes that involves
serology, check out Court TV’s Crime
Library at:
www.crimelibrary.com/criminal_mind/forensics/serology/1.html
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People of Historical Significance
Paul Kirk (1902-1970)
Professor of criminalistics and biochemistry at Berkeley
in California
He actively assisted law enforcement organizations
from 1935 to 1967.
His book, Crime Investigations, contained a chapter in
which he discussed the application of blood stain
pattern analysis to criminal investigations.
Dr. Kirk analyzed the blood stain pattern photos from
the Sam Sheppard case and was instrumental in
Sheppard’s release at his second trial. Find out more
about the case at CourtTv’s crime library.
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People in the News
Herbert L. MacDonell
Considered by many as the father of modern bloodstain
pattern analysis.
He is the director of the Lab of Forensic Science and
founder of the Bloodstain Evidence Institute (1973) in
Corning, NY.
His work, Bloodstain Pattern Interpretation, helped to
jump start this discipline.
He has consulted on criminal cases in all 50 states, in
addition to testifying in the O.J. Simpson trial and in
the assassination cases of Sen. Robert F. Kennedy
and Dr. Martin Luther King Jr.
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Blood Spatter Evidence
A field of forensic investigation which deals
with the physical properties of blood and
and the patterns produced under different
conditions as a result of various forces
being applied to the blood. Blood, as a
fluid, follows the laws of physics.
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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 travel,
 height of the perpetrator
 position of the victim
 left/right hand
 whether the body was moved, etc.
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Blood Pattern Reconstruction
Scene Pattern
Reconstruction
Lab Results
Reconstruction
1. Stain condition
1. Genetic marker typing
2. Pattern
2. Age Determination
3. Distribution
3. Source Determination
4. Location
4. Race Determination
5. Directionality
5. Sex Determination
—From “Cracking Cases” by Dr. Henry C. Lee
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Questions Answered by
Blood Spatter Interpretation
 The distance between the target surface and the origin
of blood
 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.
 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
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Bloodstain Patterns
 The crime scene investigator must
remember that the location, distribution, and
appearance of bloodstains and spatters may
be useful for interpreting and reconstructing
the events that produced the bleeding.
 Surface texture and the stain’s shape, size
and location must be considered when
determining the direction, dropping
distance, and angle of impact of a
bloodstain.
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Blood Droplet Characteristics
 A blood droplet will remain spherical in space
until it collides with 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 shape.
 How will the shape change as the height is
increased or decreased?
click to view
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Blood Droplet Volume
 A droplet contains approximately 0.05 cc
of fluid
 Is not the same for all blood droplets, but
is generally from 0.03 cc to 0.15 cc
 Is directly dependent upon the surface or
orifice from which it originates
 The impact area is called the target.
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Conditions Affecting
Shape of Blood Droplet





Size of the droplet
Angle of impact
Velocity at which the blood droplet left its origin
Height
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
Click to see
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TARGET SURFACE TEXTURE
Target surface texture
 Bloodstains can occur on a variety of
surfaces, such as carpet, wood, tile,
wallpaper, clothing…..
 The type of surface the blood strikes affects
the amount of resulting spatter, including
the size and appearance of the blood drops.
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Target surface texture
 Blood droplets that
strike a hard smooth
surface, like a piece of
glass, will have little
or no distortion around
the edge.
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Target surface texture
 Blood droplets that
strike linoleum
flooring take on a
slightly different
appearance.
 Notice scalloping
around the edge of the
blood droplets.
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Target surface texture
 Surfaces such as wood
or concrete are
distorted to a larger
extent.
 Notice the spines and
secondary spatter
present.
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Surface Texture
 In general, the harder and less porous the
surface, the less spatter.
 The softer and more porous the surface, the
more a blood drop will break apart.
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Bloodstain Patterns
(direction of travel)
 The pointed end of the
blood stain faces the
direction of travel.
Which way did the blood travel?
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Determining angles of impact
 Blood droplets in freefall have the shape of
a sphere.
 Droplets striking surfaces and leaving wellformed stains make it possible to determine
the angle at which
the droplet struck
the surface.
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Angle of Impact
 The more acute the angle of
impact, the more elongated the
stain.
 90 degree angles are perfectly
round drops 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.
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Angle of Impact
The shape of a blood drop:
 Round—if it falls straight down at a 90
degree angle
 Elliptical—blood droplets elongate as
the angle decreases from 90 to 0
degrees;
 the angle can be determined by the
following formula:
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Angle of Impact
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Point of Convergence
 The point of
convergence is the
intersection of two
bloodstain paths,
where the stains
come from opposite
sides of the impact
pattern
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Area of Convergence
(point of origin)
 The area of
convergence is the
box formed by the
intersection of
several stains from
opposite sides of
the impact pattern
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Point or Area of Convergence?
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Point of Convergence
The location of the blood
source can be determined by
drawing lines from the various
blood droplets to the point
where they intersect.
The area of convergence is
the point of origin; the spot
where the “blow” occurred. It
may be established at the
scene with measurement of
angles by use of strings.
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Origin of blood
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Image used with permission from Tom Bevel & Ross Gardner, June 2006.
Bloodstain pattern categories
(based on the mechanism that created them)
 Passive bloodstains are created when the force
acting on the blood is gravity
 Projected bloodstains occur when some form of
energy has been transferred to a blood source
 Transfer or contact is produced when an object
with blood on it comes into contact with an object
or a surface that does not have blood on it.
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Bloodstain pattern categories
PASSIVE
TRANSFER
Chapter 8
PROJECTED
82
Passive Bloodstains
 Drop(s) created or formed by the force of
gravity acting alone.
 Drops
 Drip patterns
 Pools
 Clots
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Projected Bloodstains
 Arise when a victim is subjected to blows that
produce blood released at a force greater than
gravity.
 3 subcategories:
1. Impact spatter
2. Cast-off stains
3. Arterial gush
 The size, shape and number of resulting stains
will depend, primarily on the amount of force
utilized to strike the blood source.
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Projected Bloodstains
(impact spatter)
 Created when a blood source receives a blow or
force resulting in the random dispersion of smaller
drops of blood
 Subdivided into:
 Low velocity spatter
 Medium velocity spatter
 High velocity spatter
 Back spatter
 Expiratory blood
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Low Velocity Spatter
Relatively large stains 4 mm in size and greater.
Impact velocity up to 5 feet/sec (Blunt force)
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Medium Velocity Spatter
Preponderant stain size 1 to 4 mm size.
Impact velocity of 5 to 25 feet/sec.
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Image courtesy UWA PhD research student Mark Reynolds.
High Velocity Spatter
Preponderant stain size 1 mm in size and smaller.
Mist like appearance.
Impact velocity of 100 feet/sec and greater.
(gun shot, high speed machinery)
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Projected Bloodstains
 Back spatter — blood directed back
towards the source of energy or force that
caused the spatter
 Expiratory blood — blood that is blown
out of the nose, mouth or a wound as a
result of air pressure and/or air flow which
is the propelling force.
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Gunshot: back& forward spatter
Bloodstained foam held just above target surface.
Bullet passing L to R just above sheet
bullet exits foam
Bullet enters
foam
bullet
Back-spatter
on entry
Chapter 8
Forward spatter
on exit
90
Which type of impact spatter?
The high velocity
gun shot wound
leaves a mist-like
appearance.
Chapter 8
Low and medium
Velocity, lightly
Magnified.
Low velocity blood
from the simulation of
a bleeding person
walking or running.
Note that the blood
drops “point” in91the
direction of travel
Projected Bloodstains
(cast-off pattern)
Created when blood is released or thrown from a
blood-bearing object in motion
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Arterial Spurting or Gushing
Bloodstain pattern(s) resulting from blood exiting the body
under pressure from a breached artery
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Transfer (Contact) Bloodstains
(gun, knife, hand, foot…)
 Occurs when an object contaminated with
blood comes in contact with another surface
 Examples include:
 Swipe pattern
 Wipe pattern
 Smudge
 Transfer pattern
 Blockage
 Simple direct contact
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Swipe Pattern
The transfer of blood from a moving source onto an unstained surface.
Direction of travel may be determined by the feathered edge.
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Wipe Pattern
A bloodstain pattern created when an object moves through an
existing stain, removing and/or altering its appearance.
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Transfer (Contact) Bloodstains
(Smudge)
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Transfer Pattern
A recognizable image of all or a portion of the
original surface may be observed in the pattern.
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Transfer Pattern
A recognizable image of all or a portion of the
original surface may be observed in the pattern.
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Transfer Pattern
A recognizable image of all or a portion of the
original surface may be observed in the pattern.
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Transfer (Contact) Bloodstains
(Blockage)
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Crime Scene Clean Up
View video clip about crime scene clean up
2nd video clip
Please DO NOW
1. What do you think about the “crime
scene clean up business”? Be sure to
include something specific from the
video clip.
2. Do you think you could do this?
Why or why not?
Chapter 8
102
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
the source of energy
 Cast-off—blood that is thrown from an object in
motion
Chapter 8
103
Bloodstain Terminology
 Contact stain—bloodstains caused by contact
between a wet blood-bearing surface and a second
surface which may or may not have blood on it
 Transfer—an image is recognizable and may be
identifiable with a particular object
 Swipe—wet blood is transferred to a surface which
did not have blood on it
 Wipe—a non-blood bearing object moves through a
wet bloodstain, altering the appearance of the
original stain
Chapter 8
104
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 25 feet per second, usually 100
feet per second; gives a fine mist appearance
• Medium velocity—5 to 25 feet per second
• Low velocity—up to 5 feet per second
Chapter 8
105
Tips for the Chp. 8 Test




Multiple Choice
True / False
Short Answers
What can blood stains tell
you?
 Blood Types + Typing
 (antigen— antibody)
 Blood spatter analysis
 Impact angle, shape, size,etc.
 Blood tests (precipitin, etc.)
 Blood - general information
Chapter 8
 What 3 questions are
asked at a bloody crime
scene?
 Monoclonal antibodies vs.
polyclonal antibodies
 Paternity testing
 Why might there not be
any sperm in semen?
 Sexual assault cases (what
is collected?)
106
Learning Objectives
Students should be able to :
 Contrast chromosomes
and genes.
 Use the Punnett square
to determine the
genotypes and
phenotypes of offspring.
Father’s genotype
O
O
Mother’s
genotype
A
B
V. Principles of Heredity
All of the antigens,
polymorphic enzymes and
proteins previously discussed
are genetically controlled
traits.
Principles of Heredity
 Genes (basic unit of heredity) are
located on chromosomes.
 The position a gene occupies on
a chromosome is its locus.
 Alleles are alternative forms of
genes that influence a given
characteristics (such as blood
type)
 Each cell (except for eggs and
46 chromosomes.
sperm) have _____
Click for Web Extra 8.2
Click for Web Extra 8.3
Gene Pair
 A gene pair is made up of two alleles.
 Homozygous —gene pair of 2 similar alleles
Ex. AA or BB or OO blood types
 Heterozygous —gene pair of 2 different alleles
Ex. AO or BO or AB blood types
 One gene can be dominant over the other in a gene
pair of different alleles.
Ex. A and B are dominant over O in blood types.
( O is the recessive gene)
 In AB blood type, the genes are codominant.
Click for Web Extra 8.5
Genotype and Phenotype
 Phenotype — a person’s outward appearance
 Ex. You have B type blood
 Genotype — a person’s genetic makeup for a trait
 Ex. You have BB or BO type blood.
 No blood test can determine your genotype.
 By studying the family history of an individual you
may be able to determine their genotype
Click for Web Extra 8.4
Punnett Squares and Paternity
Possible“Father’s”
genotype
O
O
Sally’s
genotype
A
AO
AO
B
BO
BO
What are the
possible blood types
for their children?
Could he be the
father of her AB
baby boy? Why or
why not?
Paternity Testing
 Disputed paternity cases are normally
encountered in civil, not criminal courts.
 Genotyping of blood antigens (factors) can be
useful in determining paternity by ruling out a
suspected “father”.
 A-B-O grouping
 HLA (human leukocyte antigen)- antigens on WBC
 If it can’t exclude a suspect than it’s better than 90% that
he’s the father
 DNA testing
 Can determine with better than 99% that he is the father
Please Do Now
Explain this cartoon.
Learning Objectives
Students should be able to :
 List the laboratory tests
necessary to
characterize seminal
stains.
 Explain how suspect
blood and semen stains
are properly preserved
for laboratory
examination.
UV light makes seminal fluids glow brightly
VI. Forensic Characterization
of Semen

Two step process for the examination of
seminal stains
1. Locate the stain
2. Test the stain to prove it’s semen
Testing for Seminal Stains
 Seminal stains may be visible on fabric due
to their stiff, crusty appearance.
 Acid phosphatase test is the best way to
locate and characterize seminal stains.
 Once sample is proven to be semen, the
next step is to associate the semen as
closely as possible with an individual
Acid Phosphatase Test
 Acid phosphatase is an enzyme secreted by
the prostate gland into seminal fluid.
 Concentration is 400X more in seminal
fluid than in any other body fluid.
 A reaction time of less than 30 seconds is a
strong indication of semen.
Testing Seminal Stains
for acid phosphatase
Moisten Stain
Activate stain
with water.
Collect Stain
Rub stain with
provided cotton
swab.
Open Test Strip Purple = semen
Test stain by
Semen is present
rubbing the
if it turns purple
moistened swab immediately.
onto test strip.
(< 30 seconds)
Microscopic Examination of Semen
 Semen is unequivocally identified
by the presence of spermatozoa.
 Usually easy to locate sperm in
semen
 Reasons why sperm might not be
found
 Sperm bind tightly to cloth material
 Sperm are extremely brittle when dry
and easily disintegrate when washed
or rubbed against another object
 Oligospermia — lows sperm count
 Aspermia— no sperm in seminal
fluid
Seminal constituents — sperm
 Live (motile) sperm generally survive for up to 4 6 hours in the vaginal cavity
 Vaginal smear must be examined microscopically
immediately after it is taken from the victim
 Nonmotile sperm may be found up to 3 days in the
vaginal cavity (occasionally up to 6 days later)
 Intact sperm (sperm with tail) are not normally
found 16 hours after intercourse (but have been
found 72 hours later)
Seminal constituents —
 Finding acid phosphatase decreases with
time after intercourse
 Little chance of identifying it after 48 hours
 Need to know if voluntary sexual activity
occurred before the assault
 p30 is NOT normally found in the vaginal
cavity beyond 24 hours after the assault
Prostate Specific Antigen
(PSA or p30)
 Positive acid phosphatase test but can’t find
any sperm — how can you prove
unequivocally that it’s semen?
 By use of p30 (prostate specific antigen,
PSA)
 Antigen — antibody reaction
 see p. 293 Figure 8-17 and Figure 8-18
Learning Objectives
Students should be able to :
 Describe the proper collection of physical
evidence in a rape investigation.
VII. Collection of Rape Evidence
 Seminal constituents on a rape victim
indicate that sexual intercourse occurred
BUT their absence does not necessarily
mean that a rape did not occur.
 Bruises and bleeding tend to confirm a
violent assault occurred
 Physical evidence of rape may include:
semen, blood, hairs and fibers
How to protect rape evidence
 Outer garments and undergarments carefully removed and
packaged in separate paper bags. WHY?
 Don’t fold an article through a seminal stain as it may
damage the sample.
 Latex gloves must be worn when collecting samples
How to protect rape evidence
(the victim)
 The rape victim must undergo a medical
examination as soon as possible after the
assault
 Use an evidence collection kit
 see p. 295 figure 8-19a and figure 8-19b and
p. 296 Figure 8-19c
Physical evidence to be collected
from scene/ victim
1.
2.
3.
4.
5.
6.
7.
Pubic combings
Pubic hair standard/ reference samples
External genital dry-skin areas
Vaginal swabs and smear
Cervix swabs
Rectal swabs and smear
Oral swabs and smear
Physical evidence to be collected
from scene/ victim
8. Head hairs
9. Blood sample (for DNA)
10. Fingernail scrapings
11. All clothing
12. Urine specimen
•
Check for Rohypnol, GHB, etc.
Physical evidence to be collected
from suspect
1. All clothing
2. Pubic hair combings
3. Pulled hair and pubic hair
standard/reference samples
4. Penile swab (within 24 hours of assault)
5. Blood sample or buccal swab (for DNA)
DNA Fingerprinting Contd…
 This will therefore
produce a unique
banding pattern
following a gel
electrophoresis.
 This test is highly
accurate, and the
probability of another
individual possessing
an identical banding
pattern is estimated as
around
1:14,000,000,000.
DNA Fingerprinting