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Forensic Science
Chapter 12: Forensic Serology
1
Karl Landsteiner
• 1901
• Figured out how to determine blood
type
• Won a Nobel Prize
2
Before blood typing
• Transfusion recipients often died
because the new blood made their
blood coagulate.
3
Blood factors
• Landsteiner created the A-B-O system
• By 1937 the Rh factor had been
identified
• Now, there are more than 100 known
blood factors
• A-B-O is still the most important for
transfusions
4
Importance of blood factors
• No two individuals, except identical
twins, could be expected to have
identical blood factors.
• Until the early 1990s, this was the best
way to link blood to an individual
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DNA
• Deoxyribonucleic acid
• Molecules that carry genetic information
• Double stranded in the shape of a
double helix
6
DNA
• Regions of DNA are now used to match
blood to individuals
• More on this in chapter 13
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Plasma
• The fluid portion of unclotted blood
• Mostly water
• 55% of blood content
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Cells in blood
• 45% of blood content
• Erythrocytes - red blood cells
• Carry oxygen to body tissues and remove
carbon dioxide
• Leukocytes - white blood cells
• Fight infections
• Platelets
• Responsible for clotting
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Serum
• The liquid that separates from blood
when it clots
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Antigens
• Chemicals on the surface of red blood
cells that give them their blood type
• Usually proteins
• Stimulates the body to produce
antibodies against it
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Antibody
• A protein that destroys or inactivates a
specific antigen
• Found in blood serum
12
Blood types
• Type A
• Has A antigens
• Type B
• Has B antigens
• Type AB
• Has A and B antigens
• Type O
• Has neither A nor B antigens
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Rh factor
• Also known as the D antigen
• Rh+ blood has the antigen
• Rh- blood doesn’t
14
Fundamental principle of blood
typing
• For every antigen there exists a specific
antibody
• Anti-A is for the A antigen
• Any antibody will only react with its
specific antigen and no other
15
Antiserum
• Blood serum in which there are specific
antibodies
• Serum from type A blood contains
Anti-B
• Serum from type B blood contains
Anti-A
• Serum from type AB blood contains neither
Anti-A or Anti-B
• Serum from type O blood contains both Anti-A
and Anti-B
16
Agglutination
• The clumping of red blood cells by the
action of an antibody
• Each antibody is bivalent – it can attach
itself to two different cells
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Why transfusions failed before blood
typing
• Example:
• Type B blood is given to a person with type
A blood
• The anti-A antigens in the type B blood
attach to the A blood cells
• They clump together
• The person dies
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Serology
• The study of antigen-antibody reactions
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Blood typing
• Blood of unknown type is mixed with a
known antiserum and checked for
agglutination
Anti-A
Serum +
whole
blood
Anti-B
serum +
whole
blood
Antigen
Present
Blood Type
+
-
A
A
-
+
B
B
+
+
A and B
AB
-
-
Neither A
nor B
O
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Blood types in the US
• Blood type distribution varies throughout
the world
• In the US, 43% have O blood, 42%
have A, 12% have B, and 3% have AB.
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If type O blood contains anti-A and anti-B then why can it be given to
people with type A blood or type B?
• In extreme situations type O negative blood would be
the best choice for an emergency transfusion, but in
all other situations blood should be accurately crossmatched before transfusion. Type O blood contains
serum anti-A and anti-B antibodies which potentially
could react with the recipient’s blood cells and
produce harmful side-effects such as clumping of red
cells. However, since most transfusions consist of
adding a relatively small volume of donor blood to a
larger volume of recipient blood, dilution of the
donated antibodies occurs and this reduces the
degree of adverse reactions to a manageable or
insignificant level.
•
http://www.nurseminerva.co.uk/blood1.htm#q5
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Drug antibodies
• Can be produced
• Used to test blood and urine for drugs
23
EMIT
• Enzyme-multiplied immunoassay
technique
• Can detect even trace amounts of drugs
in urine
• May give false positives by reacting with
chemicals similar to the drugs – other
tests are needed
24
Polyclonal antibodies
• Antibodies that attack different sites on
the same kind of antigen
• Produced by injecting animals with
antigens
• May change over time
25
Monoclonal Antibodies
• Identical antibodies that interact with a
single antigen site
• Require more manipulation after animal
is injected with antigen
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Bloodstain questions
• Is it blood?
• Is it human?
• Can it be matched to one person?
27
Benzidine color test
• Formerly used to test for the presence
of blood.
• Benzidine is a carcinogen
• No longer used
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Kastle-Meyer test
• Uses phenolphthalein to test for blood
• When blood is mixed with
phenolphthalein solution and hydrogen
peroxide, it turns a deep pink color
• Some other substances, like potatoes
and horseradish, will also turn pink
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Hemoglobin
•
•
•
•
In red blood cells
Makes them red
Carries oxygen
Makes the Kastle-Meyer test work
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Hemastix
• Used to test urine for blood
• Can be used to test bloodstains
• Turn green when there is blood
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Luminol testing
• Sprayed on objects in a darkened room
• If there is blood, it will luminesce (give
off light)
• Can detect even very diluted blood
• Will not interfere with DNA testing
32
Precipitin test
• Used to determine what animal blood
came from
• Adding various antiserums (human,
dog, cat) to blood samples
• If the antiserum causes the blood to
precipitate and get cloudy, it was the
correct animal.
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Classic method
• Put blood sample on top of human
antiserum in a capillary tube.
• If it is human blood, a cloudy ring or
band will form where the two
substances meet
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Gel diffusion
• Antibodies and antigens will move
towards each other on an agar-gel
coated plate
• They are placed in separate spots on
the plate.
• If they move towards each other and
form a precipitin line, then they match
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Precipitin test
• Very sensitive
• Blood can be diluted or old
• Has been successful on mummies
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Individualizing blood
• Blood type
• Enzymes
• Proteins that have important functions in
the body’s chemical reactions
37
Polymorphism
• The existence of more than one form of
a genetic trait
• Polymorphic enzymes exist in different
forms
38
Iso-enzymes
• Multiple forms of an enzyme having the
same or very similar activities
39
Example: PGM
• Not everyone has the same PGM isoenzymes
• 3 variations
• Helps reduce the number of possible
matches
40
Using enzymes on bloodstains
• Only the ones that survive drying and
aging are useful
• The more factors a serologist can
identify, the better they can narrow
down a sample
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Bloodstain patterns
• Factors that can help interpret and
reconstruct events
• Location
• Distribution
• Appearance
• Position
• Shape
• Analysis requires carefully planned control
experiments
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Surface texture
• Patterns and matches are only valid if
identical surfaces are used
• Hard and less-porous surfaces result in
less spatter
43
Direction of travel
• Can be determined from stain’s shape
• Pointed end always faces direction of
travel
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Impact angle
• Can be determined on a flat surface
• Measure circular distortion
• Right angles produce circular drops
• As the angle decreases, the elongation
increases
45
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Origin of blood spatter
• Draw straight lines through the long axis of
several drops
• Where the lines meet is where the blood
came from
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Genes
• Control all the antigens and enzymes
• A unit of inheritance
• A DNA segment on a chromosome
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Chromosomes
•
•
•
•
Threadlike structures in the cell nucleus
Hold genes
Made of DNA and proteins
Human cells contain 46 chromosomes
in 23 pairs
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Reproductive cells
•
•
•
•
Contain only 23 chromsomes
Egg – female cell
Sperm – male cell
Zygote – combined egg and sperm
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Sex chromosomes
• X chromosome – female
• Y chromosome – male
• Shorter than X
• The mother always contributes an X
chromosome. (females are XX)
• The father can contribute an X or a Y.
(males are XY)
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Locus
• The position a gene occupies on a
chromosome
• Genes for the same trait from the two
parents are next to each other
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Alleles
• Alternative forms of genes that control
the same traits
• Example: blood type has A, B, and O
alleles
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Homozygous
• A gene pair of two similar genes
• AA or BB or OO
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Heterozygous
• A gene pair of two different genes
• AO or BO or AB
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Genotype
• The combination of genes
• AO
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Phenotype
• What the trait looks like
• Type A blood
• Could be AA or AO
57
Punnet squares
• Predict the possible genotypes and
phenotypes of offspring
• Examples: father is AO, mother is AB
• Father is OO, mother is BO
• No gene can appear in a child unless it
is present in at least one of the parents
58
Paternity testing
• Usually civil, not criminal cases
• Involves blood factors other than just
blood type
• Now use DNA
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Locating semen stains
• Sometimes you can see it easily
• If not, use the acid phosphatase color
test
60
Acid phosphatase
• Enzyme present in seminal fluid in great
concentration
• Up to 400 times greater than other bodily fluids
• Can be tested with various solutions, with or
without UV light
• Some other substances – fruits and veggies,
fungi, contraceptive creams, and vaginal
secretions may give positive results, but not
as fast or not as strong
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Spermatozoa
• Sperm
• Can be seen through a microscope –
means the stain was definitely from
semen
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Locating sperm in a stain
• Put the fabric in a little water and stir
• Some sperm will come off in the water
and can be seen under the microscope
• Sperm can be bound tightly to fabric
• Sperm are very brittle when dry – can be
easily destroyed
63
Medical abnormalities
• Oligospermia
• Low sperm count
• Aspermia
• Absence of sperm (sterility)
• Natural or after a vasectomy
64
Semen without sperm
• Can still be identified as seminal fluid
using a protein called p30 or PSA
(prostate specific antigen)
• Unique to seminal fluid
• Detected with antibodies
65
Rape evidence
• Semen is not enough
• Presence just means there was sex
• Absence could mean a condom was used
• Bruises or bleeding indicate violence
• Possible transfer of physical evidence
• Blood and semen
• Hairs and fibers
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Protecting evidence
• Preserve all outer- and undergarments
in paper bags
• Have the victim stand over a large piece
of paper when disrobing to collect loose
foreign material
• Bedding or other objects from the scene
may be collected as evidence
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Medical examination
• As soon as possible
• By trained professional (nurse or doctor)
• Pubic combings
• For foreign hairs
• Pubic hair reference samples
• Cut 15 – 20 hairs at the skin line
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• Vaginal swabs and smear
• When warranted by case history
• Two simultaneous swabs – let dry
• Two more swabs are smeared on slides – let dry
• Rectal swabs and smear
• When warranted
• Two simultaneous swabs, one kept and one
smeared – let dry
• Oral swabs and smear
•
•
•
•
When warranted
One swab for buccal area, one for gumline
Both swabs get smeared on one slide
Let dry
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• Head hairs
• At least 50 hairs from different areas of the
heat - cut at skin line
• Blood sample
• DNA and toxicology testing
• Fingernail scrapings
• Use dull object to collect debris from under
nails
• All clothing
• Urine sample
• Drug testing
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Saliva samples
• Can be used for DNA
• Recovered with a damp swab followed
by a dry swab
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Collected from suspect
• Clothing
• Victim’s DNA may be present in underwear
• Pubic hair combings
• Pulled head and pubic hair reference
samples
• Penile swab if within 24 hours of assault
• Blood sample or buccal swab for DNA
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Testing for sperm in the victim
• Motile sperm last for 4 – 6 hours
• Requires immediate examination of vaginal smear
• Nonmotile sperm can last for 3 – 6 days.
• Intact sperm (with tails) usually only last 16
hours, but have been found as late a 72
hours later
• Seminal acid phsophatase can last for 48
hours
• p30 can last for 24 hours
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