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2009©Forensic Science Today
Serology
Body fluids and the stains they leave at crime scenes
2009©Forensic Science Today
Common Types of Serology
Commonly found rape cases are: Blood Hair Sperm
2009©Forensic Science Today
History of Blood Typing 1901- Karl Landsteiner, recognized
differences in human blood Received Nobel Prize in 1929 Critical in blood transfusions A-B-O classification system Rh factor in blood was demonstrated
in 1937 More than 100 different blood factors
are known today.
2009©Forensic Science Today
True or False
No two individuals, except for identical twins, could be expected to have the same combination of blood factors.
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Prior to 1990, A-B-O system provided the best means for forensic scientists to link blood to an individual.
What changed in 1990?
2009©Forensic Science Today
Components of Blood
Cellular-Solid materials suspended in plasma that makes up 45% of “blood” Red Blood Cells (RBC)-erythrocytes White Blood Cells (WBC)-leukocytes Platelets
Plasma – 55%- fluid portion of unclotted blood-mostly water Antibodies Enzymes Proteins
Serum= liquid that separates from the blood when a clot is formed
2009©Forensic Science Today
Blood Stains on Victim’s JeansSections removed & initialed for testing
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Forensic Characterization of Bloodstains
Is it blood? From what species did it originate? If the blood is of human origin, how
closely can it be associated to a particular individual?
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Species Identification
Prior to 1990, double immuno-diffusion plate was used for species identification of blood stains.
Today scientists simply test using DNA techniques
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Techniques to Visualize Kastle-Meyer – uses H2O2 +
phenolphthalein to produce a bright pink color in the detection of peroxidase activity in blood
Leucomalachite green. Leucomalacite green is dropped on the suspect stain. A positive blood result will immediately turn the swab greenish-blue.
2009©Forensic Science Today
More Visualization Tetramethylbenzidine- test by placing drops
on a suspect stain. A positive reaction is indicated by an intense blue color.
Luminol- Luminol is also a field test that you may have seen on one of the forensic investigation television shows. It involves spraying the chemical onto the suspected bloodstain and viewing it in total darkness. If blood is present, it will begin to luminesce (glow a whitish-blue) within 5 seconds.
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Luminol Test Extremely Sensitive- capable of detecting
bloodstains diluted up to 300,000 times Large areas are sprayed and viewed in
darkened areas for emission of light Does not interfere with subsequent DNA testing http://www.flickr.com/photos/jackofspades/4376209354/ Figure 12-5 p. 337 Saferstein Criminalistics, 2004
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A Bloody Knife from a Homicide Scene.
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From what species did it originate?
Preciptin Test >Very sensitive
>Requires only a small sample>Even dried bloodstains from 10-15 years ago can be tested.
>Positive test results even in diluted samples Gel diffusionSee pp. 338-339 Saferstein, Criminalistics, 2004.
2009©Forensic Science Today
Applications of Genotyping Blood Factors
No direct relevance to Criminal Investigations
Paternity Testing Blood type may clear a suspectExample: Child is type ABMother is type AB Suspected Father is type ODraw the Punnett Square.
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Rape Statistics
http://www.rainn.org/statistics
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Forensic Characterization of Semen
Locate the stain and screen for semen with the acid phosphatase color test
Acid phosphatase is an enzyme present in high concentrations in semen
Suspect stain is transferred to filter paper; reagent is added. If semen is present, sample will fluoresce under UV light within 30 seconds.
http://www.houstonpi.com/sementrace/videos.html
2009©Forensic Science Today
Microscopic Examination
Semen can be identified by the presence of spermatazoa @ 400x magnification
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Challenges for the Microscopist
Sample collection: Sperm bind tightly to cloth materials, are extremely brittle when dry, and disintegrate if the stain is washed or rubbed against another object
Oligospermia – abnormally low sperm count (prefix Oligo means “just a few or scant”
Aspermia- absence of sperm or sterility (partly due to growing popularity of vasectomies)
2009©Forensic Science Today
p30 or Prostate Specific Antigen Protein discovered in 1970’s Unique to seminal plasma See Criminalistics pp. 351 & 352
Figure 12-6 and Figure 12-17 for PSA testing by precipitation and electrophoresis
If semen is present, DNA testing is used to link seminal material to an individual. More later. . . .
2009©Forensic Science Today
Collection of Rape Evidence Forceful physical contact between victim
and assailant may result in the transfer of hair, fibers, blood, and semen (Locard’s Exchange Principle)
Carefully package all outer garments and undergarments separately in PAPER bags.
Victim should stand on paper while undressing so that any loose fibers can be collected for analysis.
Collect bedding, if appropriate
2009©Forensic Science Today
Collection of Rape Evidence
Disposable latex gloves are essential for handling evidence!
DNA may be transferred through perspiration. Investigators must avoid direct
personal contact with evidence.
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Victim needs a medical exam ASAP! Evidence collection kit includes Pubic combings & standard/reference samples External genital skin areas Vaginal swabs & smear Cervix swabs Rectal swabs & smear Oral swabs & smear Head hairs Blood sample Fingernail scrapings All clothing Urine specimen (for drug testing e.g. Rohypnol, GHB) Swab of any area that may have assailant’s saliva for DNA
testingSee Saferstein, Criminalistics, 2004, p. 353
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Evidence from Suspect, if apprehended
All clothing Pubic Hair combings Pulled head and pubic hair
standard/reference samples Penile swab taken within 24 hours
after assault Blood sample or buccal swab for DNA
testing
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DNA Testing
Extremely sensitive- characterization possible with only 1 billionth of a gram of sample
2009©Forensic Science Today
Timing Sperm can survive up to 4-6 hours in the
vaginal cavity of a living female. Time of sexual attack may be determined. Nonmotile sperm may be found up to 3
days after intercourse. Acid phosphatase can be detected in the
vaginal cavity for up to 48 hours after intercourse. p30 can be detected for 24 hours.
2009©Forensic Science Today
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