62 Science of Crime Scenes 1 Biological Evidence Distinction between body fluids and tissues and DNA Biological materials Blood hair semen saliva etc Molecular information DNA Biological materials are also useful for toxicological examinations ID: 912824
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Slide1
Science of Crime Scenes
Chapter 6.2
Science of Crime Scenes
1
Slide2Biological Evidence
Distinction between body fluids and tissues and DNABiological materials: Blood, hair, semen, saliva, etc.
Molecular information: DNABiological materials are also useful for toxicological examinations
Science of Crime Scenes
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Slide3DNA
Dexoxyribonucleic acid (DNA) is a molecule present in every living
cellencodes the information
needed for the development and the
life
cycle of organisms
DNA appears as a double helix of about 6 billion paired
nucleotides
E
ach made of a phosphate associated with a sugar on which is linked one of the following four bases:Guanine (G)Cytosine (C)Thymine (T)Adenine (A)Bases constitute the links between the two sides of the helix chainAdenine only bonds to ThymineCytosine only bonds to Guanine
Science of Crime Scenes
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Slide4DNA
The quantity of DNA present in each cell is about 6 picograms
6.10-12 g0.6 ng (6.10
-10
g)
produces
a DNA profile of good
quality
Which
means that only about 100 cells are requiredEven if such a small quantity of DNA is collected and later profiled, what does it mean to have found so low an amount of material?Science of Crime Scenes4
Slide5Collection
Porous materials are easy; the cells are trapped in the materialNon-porous materials are more difficult; recommended protocol:
Photograph any perishable pieces of information that may be destroyed by swabbing
Using a sterile cotton swab that has been soaked with distilled water and from which excess water has been removed, swab the surface
aggressively
Document
details regarding the exhibit description and area(s) swabbed.
Air-dry in a cabinet to prevent
contamination
Once dried, transfer the swab into a DNA tube for processingScience of Crime Scenes5
Slide6DNA collection on non-porous surface
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Slide7Blood
A human being has about 5 liters of bloodBlood is a matrix of free cells (red, white globules) and anticoagulant platelets carried by the plasma (the liquid portion
)Plasma is about 55%
water
Red
blood cells (erythrocytes) compose
99% of the solid elements of
blood
Not
really “cells,” as they do not possess a nucleusCarry oxygen through hemoglobin, which uses iron to bond the oxygenThe iron is targeted for presumptive tests for bloodScience of Crime Scenes7
Slide8Where does the DNA come from?
White cells (leukocytes) and platelets compose approximately 0.3% and 0.7% of the solid elements of blood
The former are dedicated to combating infectious agentsLeukocytes are
the only ones containing DNA
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Slide9Detection of blood
Bluestar® forensic reagent, based on Luminol
, is presently the most efficient commercial product for visualization of suspected blood at the crime sceneEasily
sprayed, it can also be used for spot tests with cotton swabs
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Slide10Blood detected by Bluestar
on fenceScience of Crime Scenes
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Slide11Bloody shoeprint developed with Bluestar
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Slide12Spatter patterns
Can be illustrative of the points of origin and determining where they intercept a target
surfaceThe direction of travel can be determined by the direction of the greatest edge distortion
SAADD
A: Alignment of individual spatters with respect to the whole pattern
A: Alignment of individual spatter stains with respect to each other
D: Distribution (density) of the number of spatters
D: Distribution (frequency) of spatter size ranges
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Slide13Science of Crime Scenes
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Slide14Science of Crime Scenes
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Slide15Semen
Semen is a mixture of various fluids that carry live spermatozoa to the female ovule for fertilization
A fertile semen sample holds tens of millions of spermatozoa per milliliterVarious spermatozoa nutrients are immersed in the seminal fluid
Proteins
(vitamins and phosphatase
)
Mineral salts
Testosterone
Provides
useful DNA evidence, due to the DNA contained in the spermatozoa headScience of Crime Scenes15
Slide16Duration for collection
Viable semen for forensic analysis can found: 19
days in the cervix10 days in the vagina110 hours in the
rectum
44
hours in the
anus
31 hours in the mouth
The presence of
spematozoa is conclusive for sexual contactScience of Crime Scenes16