Transcript blood/dna

Blood, Blood spatter and DNA
Ch. 7 and 8
Forensic blood video
Blood spatter video
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Dexter-
23456*
Science of Murder- blood *
Blood typing
If blood is found at the scene of a crime, it can
be tested for blood type. This may narrow down
suspects
 – Cheaper, easier, and faster than DNA testing ,
which provides individual evidence
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Blood spatter
A spatter pattern can give information about
the truthfulness of an account by a witness
or a suspect
 It also can provide information about the
origin of the blood, the angle and velocity of
impact and type of weapon used
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Composition of Blood
Whole blood has cells and plasma (fluid with
hormones, clotting factors and nutrients)
 Red blood cells carry oxygen to the body’s
cells and CO2 away
 White blood cells fight disease and foreign
invaders
 Platelets aid in blood clotting
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What is blood typing?
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Antibodies are proteins secreted by white blood
cells that attach to antigens to destroy them
(defense machanism)
Antigens are foreign molecules that react to antibodies
(causes agglutination or clumping)
In this case, antigens are carbohydrate tags on red blood
cells that are read by your immune system
If your immune system recognizes them, everything is
fine
If your immune system sees them as foreign, it attacks!
A person with type A blood has A antigens on
the surface of their red blood cells.
 A-type individuals do not make antibodies
against A antigens.
 A-type individuals make antibodies against B
antigens
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If a person with Type A blood receives a Type B
transfusion, the anti-B antibodies will bind the B
antigens
 Donor cells are destroyed by complementmediated lysis
 Can lead to jaundice and kidney damage
 Death
 Therefore, they can only receive A or O blood
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A person with type B blood has B antigens on
the surface of their red blood cells.
 B-type individuals do not make antibodies
against B antigens.
 B-type individuals make antibodies against A
antigens
 Can only receive B or O blood
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A person with type AB blood has A and B
antigens on the surface of their red blood cells.
 AB-type individuals do not make antibodies
against A or B antigens.
 Can receive A, B, AB, or O blood
 – Called the universal recipient
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A person with type O blood has no antigens on
the surface of their red blood cells.
 O-type make antibodies against A and B
antigens
 Can only receive other O blood, but can donate
to all other blood types
 – Known as the universal donor
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Type
A
B
 AB
O
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Percent
39
12
4
45
What is Rh factor?
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Rh Factor is another antigen present on RBCs
– it’s where the +/- of your blood type comes from
– named after the Rhesus Monkey (where they were
first discovered)
Can cause problems with transfusions
– Rh negative people can’t receive positive blood (get
an antigenic reaction- destruction of cells)
Also get similar reaction when Rh-negative
mother is carrying an Rh-positive fetus
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If the sample clots, then the antibodies are binding, so
the antigen must be present
– If Anti-A makes it clot, A is present –>A (AB)
– If Anti-B makes it clot, B is present –>B (AB)
– If both Anti-A and Anti-B samples clot, Both antigens
are present –> AB
– If neither Anti-A or Anti-B makes it clot, neither
antigen is present –> O
– If Anti-Rh makes it clot, Rh factor is present -> +
Human Blood Testing
Blood Compatibility
Is that Blood
Luminol Presumptive test
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The first step in an investigation.
Seen on most CSI TV shows as the blue
glowing light test.
Presumptive Test: Possibility that it is blood
or it is not blood.
It uses luminol, a peroxide and a base.
Presumption Blood Testing
(using the kastel-meyer video)
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Kastel-Meyer Blood Test
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It will not prove that a sample is definitely blood, it
simply supports the idea that the sample could be blood
Kastel-meyer is used because of ease of use, doesn’t
destroy DNA and is very sensitive (can detect 1 drop in
10,000 drops), positive test results in easily seen color
change due to presence of hemoglobin
Uses alcohol, phenophthalein (special prep- not the kind
used in acid/base testing) hydrogen peroxide.
It undergoes a oxidation-reduction reaction
Look for no color change with the addition of alcohol
and phenophtalein and blue color with hydrogen
peroxide
Blood Spatter (dexter explain)
(blood spatter interpretation)
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Splatter is the sound a liquid makes when it
comes in contact with an object
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Spatter is the pattern blood makes on an
object
Blood spatter
The pattern can help to reconstruct the
events surrounding a shooting, stabbing or
beating
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Direction blood traveled
 Angle of impact
 Point of origin of the blood
 Velocity of the blood
 Manner of death
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Common Bloodstain Patterns
Walking Drip Pattern
 Wipes
 Swipes
 Transfer Stains
 Arterial Spurts (vertical & horizontal)
 Cast-off Spatter
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When blood falls from a height or at a high
velocity, it can overcome its natural
cohesiveness and form satellite droplets
 When it falls onto a less-than-smooth
surface, it can form spiking patterns
around the drops
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Directionality
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The shape of an individual drop of blood
provides clues to the direction from where it
originated
Shapes
www.deviantcrimes.com/bloodspatter.htm
Gun
Hammer
http://www.clt.uwa.edu.au/__data/page/11250
8/fsb05.pdf
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Low Velocity - This type of spatter is usually caused by an
impact to the blood source at a rate of 5 feet per second
and is usually about 4 millimeters in diameter.
(victim walking)
Medium Velocity - This type of spatter is usually caused by
an impact to the blood source at a rate of 5-100 feet per
second. Stains caused by this type of force are usually 1-3
millimeters in diameter, but may be larger or smaller. (batstab)
High Velocity - This type of spatter is usually caused by an
impact to the blood source in excess of 100 feet per
second and is usually less than 1 millimeter in diameter,
although it can be larger or smaller.
(gun)
Angle of Impact
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http://www.bloodspatter.com/BPATutorial.htm
Creating Reference Bloodstain
Patterns
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http://bloody2.com/diameter.aspx
Blood spatter video
Dexter-
23456
Science of Murder- blood
DNA Fingerprinting
A more modern and popular approach,
 DNA fingerprinting can be very conclusive
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Alec Jefferys
 DNA evidence
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DNA can be isolated from
many sources:
Blood
Semen
Saliva
Hair
Skin cells
Bone
Teeth
Tissue
Urine
Feces
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Vomit
Condoms
Hat bands
Bras
Cigarette Butts
Chewing gum
Envelopes
Drinking Cups
Under victim’s fingernails
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Running DNA Video
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Death, drugs, driving and DNA: Forensic
Potpourri (you tube or Research Channel)
PCR (Polymerase Chain Reaction) is used to
make a small amount of DNA (like you’d find at
the SOC) into a large amount for testing
 Restriction enzymes are used to cut the DNA
into fragments at specific sites
 Gel Electrophoresis is used to separate the
fragments into a pattern called a fingerprint
 These fingerprints can be matched to
fingerprints from DNA isolated from suspects
(usually by mouth swab)
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DNA STRAND:
CTGGCTAGGCTACCATGCCCGTAAAT
 Everyone has unique DNA except twins
Restriction Enzyme
We will use TA-ase, an imaginary enyzme, to
cut our DNA
 Sample DNA strand
 CTGGCTAGGCTACCATGCCCGTAAAT
 CTGGCTA GGCTA CCATGCCCGTA
AAT
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Electrophoresis
Separates fragments by size
 Largest fragment travels least
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Gel electrophoresis separates the resulting
fragments by size
 – the largest fragment moves the slowest through
the gel so it stays up at the top
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And we get a fingerprint that looks something
like this:
Fingerprints can then be compared to decide
which DNA is which
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OJ crimes of the century (DNA)
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http://www.biology.arizona.edu/human_bio/p
roblem_sets/DNA_forensics_2/DNA_forensi
cs.html
http://www.biologycorner.com/bio4/notes/DN
A_fingerprint.php
 http://www.dnai.org/index.htm
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