Transcript Forensic Serology

The study of antigen-antibody reactions
The Nature of Blood-1
 Blood is a complex mixture of:
 Cells
 Enzymes
 Proteins
 Fluid Portion is called Plasma
 Mostly water
 accounts for 55% of blood
 Cells Suspended in Plasma
 Erythrocytes (Red Blood Cells)
 Leukocytes (White Blood Cells)
 Platelets
The Nature of Blood-2
Antigens and Antibodies
 RBC’s
 transport O2 from the lungs to body tissues
 May have antigens on surface
 Antigens are grouped into the ABO and Rh systems.
 Type A-has A antigens on it’s surface
 Type B-has B antigens on it’s surface
 Type AB-contain both A and B antigens on its surface
 Type O-has neither antigens on it’s surface
The Nature of Blood-3
Antigens and Antibodies cont.
 Rh Factor- person can be Rh+ or Rh Rh+: has D antigen on its surface
 Rh-: does not have D antigen on its surface
 For every antigen there is an antibody
 Anti-A
 Anti-B
 Anti-D
 Antibodies only react with its specific antigen and no
other.
 See Figure 8-1 pg 270 (Draw, color, and label)
The Nature of Blood-4
Antigens and Antibodies cont.
Blood Type
Antigen on RBC
Antibodies
A
A
Anti-B
B
B
Anti-A
AB
AB
Neither
O
Neither
Both
The Nature of Blood-5
Blood Typing
 Blood typing is accomplished by using 2 serums: Anti-
A and Anti-B
Distribution of Blood Types in the US
O
A
B
AB
43%
42%
12%
3%
Forensic Characterization of Bloodstains-1
 The science of bloodstain analysis somewhat traditionally
follows certain steps which serve to adequately describe the
various tests conducted.
 Those steps are:
1. Is the sample blood?
2. Is the sample animal blood?
3. If animal blood, from what species?
4. If human blood, what type?
5. Can the sex, age, and race of the source of blood be
determined?
Forensic Characterization of
Bloodstains-2
 Color Tests
 Benzidine test- used in the past, but has been identified
as a carcinogen
 Kastle Meyer test-turns a deep pink in the prescence of
blood due to rxn b/w blood, phenolphthalein, and
H2O2.
 Hemastix test-field test that when moistened with
distilled H2O and placed in contact w/ blood turns
green.
Forensic Characterization of
Bloodstains-3
 Luminol
 Extremely sensitive test
 In the presence of blood,
produces a light rather than a
color.
 Produces a faint blue glow
 Can easily be sprayed over large
areas
 Does NOT interfere w/ any
subsequent DNA testing
Forensic Characterization of
Bloodstains-4
 Microcrystalline Tests
 Makes ID of blood more specific.
 Depends on addition of chemicals to produce crystals
 Less sensitive than color tests and susceptible to
contaminants.
 Two most popular tests: Takayama and Teichmann
Forensic Characterization of
Bloodstains-5
 Precipitin Test
 Antibody-antigen reaction
forms a precipitate.
 Helps distinguish if blood
is from human or of other
animal origin.
 Based on the fact that
when human blood is
injected into a rabbit
antibodies form to
neutralize it’s presence.
 The animal is bled and the
blood serum is isolated
and is known as human
antiserum.
Forensic Characterization of
Bloodstains-6
 Gel Diffusion
 Electrophoresis is used to move antigens and antibodies
towards each other.
 The extracted bloodstain and human antiserum are
place in separate holes opposite each other on the gel.
 If the blood is human, a line of precipitation forms
where the antigens and antibodies meet.
Immunoassay Techniques-1
 Produces antibodies that
reacting with drugs
 A specific drug and
protein are combined and
injected into an animal
(rabbit or mouse).
 Drug-protein complex acts
as an antigen stimulating
the animal to produce
antibodies.
 The recovered blood
serum form the animal
now contains antibodies
specific to the drug.
Immunoassay Techniques-2
Types
 RIA (Radioimmunoassay) Drugs are labeled w/ radioactive tags
 There are questions about the reliability of RIA
 EMIT (Enzyme-Multiplied Immunoassay Technique) Drugs are labeled w/ an enzyme tag
 Adding urine antibodies that bind to a type of drug
being looked for.
 A chemically labeled version of the drug is added.
 Competition between the labeled and unlabeled to bind
w/ the antibody occurs-signifies urine screen test is
positive.
Bloodstain Patterns-1
 Useful in reconstructing
the events that produce
bleeding.
 Analysis of bloodstain
patterns is extremely
complex.
 Interpretation of
bloodstain patterns
necessitates carefully
planned control
experiments using surface
materials comparable to
those found at the crime
scene.
Bloodstain Patterns-2
 Important observations and conclusions to be considered.
Bloodstain Patterns-3
Principles of Heredity-1
Genes and Chromosomes
 Hereditary material is transmitted by a molecule called
DNA that is composed of genes.
 Genes control the development and growth of every body
structure.
 DNA tightly coils into structures called chromosomes.
 Chromosomes are found in the nucleus of every cell.
 All body cells in a human have 46 chromosomes (23 pairs)
2 of the 46 determine gender.
 Sex cells (egg or sperm) have 23 chromosomes.
 Fertilization
 Occurs when a sperm and egg combine
 Girl=XX Boy=XY
Principles of Heredity-2
Genes and Chromosomes
 Alleles
 Alternative forms of a gene.
 Ex: Blood Type (controlled by 3 genes A,B and O)
 Combinations:






AA=homozygous dominant for type A blood
AO=heterozygous for type A blood
BB=homozygous dominant for type B blood
BO=heterozygous for type B blood
AB=heterozygous for type AB blood
OO=homozygous recessive for type O blood
Principles of Heredity-3
Genes and Chromosomes
 Genotypes and Phenotypes
 Genotype-genetic makeup of an individual (the letters)
 Phenotype-physical appearance as a result of the
genotype (appearance)
 Ex: The letters AA are the genotype. The appearance as
a result of the genotype is Type ____ blood.
Father
 Practice Punnett Squares
Father
M
o
A
T
h
er B
O
O
M
O
T
h
E
R
O
O
A
AO AO
B
BO BO
Principles of Heredity-4
Paternity Testing
 Disputed paternity can be resolved by comparing
blood group genotypes of suspected parents.
 If a child has AB blood it is unlikely he is the father:
O
O
A
AO
AO
B
BO
BO
 Combined with HLA (human leukocyte antigen) test
and DNA testing the odds of establishing paternity are
beyond 99%
Forensic Characterization of Semen-1
Testing for seminal stains
 Acid Phosphatase Test Moistened filter paper is rubbed lightly over suspect
areas. One or two drops of sodium alphanaphthylphosphate and Fast Blue B dye are added to the
paper. The paper will turn purple if acid phosphatase is
present.
 Acid phosphatase is an enzyme found in semen.


Secreted by the prostate gland
Presence is indicated when it comes in contact with an acidic
soln. of sodium alpha naphthylphosphate and Fast Blue B dye.
Forensic Characterization of Semen-2
Testing for seminal stains
 Microscopic Examination of Semen
 Identified by presence of spermatozoa via microscopic
examination.
 Spermatozoa are slender, elongated cells with a thin
flagellate tail.
 Are usually easily located, but will bind tightly to cloth
materials.
 Stained material can be placed in water and stirred.
Spermatozoa will be present in the volume of water and
some water can be extracted and dried onto a
microscope slide, stained and examined under the
microscope.
Forensic Characterization of Semen-3
Testing for seminal stains
 Prostate Specific Antigen
 Protein that allows specific identification of semen.
 Unique to seminal plasma.
 Semen and anti-p30 are placed in wells. The antigen
and antibody move toward each other. If a visible
precipitation line forms it is proof the stain is seminal in
nature.
Collection of Rape Evidence-1
 Medical examination of a rape victim must occur
immediately after an assault.
 Outer and undergarments from those involved are
carefully removed and packaged separately in paper
bags.
 Victim is placed on a clean sheet and asked to remove
clothing. All foreign material will drop on sheet.
Clothing is packaged appropriately.
 Bedding or the object on which the assault took place
should be submitted for processing.
Collection of Rape Evidence-2
 Items containing stains should not be folded due to
flaking of the stain.
 Objects to large to submit to the lab should be cut and
sent with a piece that does not contain a stain for a
control.
 In the lab seminal stains are linked to a donor using
DNA typing.
Collection of Rape Evidence-3
 Physical evidence that MUST be collected:
 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
 Head hairs
 Blood sample
 Fingernail scrapings
 All clothing
 Urine specimen
Collection of Rape Evidence-4
 If suspect is apprehended the following is
collected:
 All clothing
 Pubic hair combings
 Pulled head and pubic hair standard/reference samples
 Penile swab
 Blood sample or buccal swab