Transcript DNA Analysis - Cobb Learning

DNA & Blood Spatter Analysis
Blood Splatter
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When a wound is inflicted, a blood splatter
pattern may be created.
A group of blood stains makes a blood
splatter pattern.
Used to reconstruct the events surrounding a
shooting, stabbing, or beating.
Blood Splatter Analysis
Analysis of a splatter pattern can aid in
determining the:
– direction blood traveled.
– angle of impact.
– point of origin of the blood.
– velocity of the blood.
– manner of death.
Blood Splatter Analysis
• Satellite droplets
– blood falls from a height or at a
high velocity
– it can overcome its natural
cohesiveness
• Spiking pattern
– Blood falls onto a less-thansmooth surface,
Blood Splatter Analysis—Six
Patterns
Describe each of these:
a. passive drops
b. arterial gushes
c. splashes
d. smears
e. trails
f. pools
Blood Splatter Analysis—
Impact
Patterns can help investigators determine
the type of weapon used.
Blood Splatter Analysis—
Directionality
The shape of an individual drop of
blood provides clues to the direction
from where the blood originated.
Blood Splatter
Analysis—Location of the
Origin of the Blood
Lines of convergence
• Draw straight lines down the axis of
the blood splatters.
• Where the lines converge, the blood
originated.
Crime Scene Investigation
of Blood
1. Search for blood evidence.
2. If any is discovered, process it determining:
a. Whether the evidence is blood.
b. Whether the blood is human.
c. The blood type.
3. Interpret the findings:
a. See if the blood type matches a suspect.
b. If it does not, exclude that suspect.
c. If it does, decide if DNA profiling is needed.
Forensic Serology & DNA
• The examination and analysis of the
properties and effects of body fluids
– Used primarily as screening tool
• DNA analysis: identification
• Biological evidence includes:
– Blood, semen, saliva, sweat, urine, fecal matter
– Bone, tissue, fingernail clippings
Analysis of Biological Stains
• Visual Examination/ Enhancement
– Crime Scenes ( in situ)
• Locate visible stains characteristic of blood or other fluids
– Locating & defining areas of stain
• Alternate light sources (black light)
– Blood Enhancement chemicals
• Not specific
• Chemiluminescence or Fluorescence
• Presumptive Tests
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Easy
Quick
Very sensitive
Crime scenes & Laboratory
Not very specific (false positives)
Identification of Blood
• Most blood tests rely on
characteristics of hemoglobin
– Heme
• Large ring structure with Fe at
center
– Peroxidase Peroxidase-like
activity of heme
• Provides catalyst for oxidation of
normally colorless substrates in
presence of hydrogen peroxide
Uses of DNA Analysis
• Paternity testing
– identifying father
• Historical investigations
• Missing persons investigations
• Mass disasters
– putting pieces back together
• Military DNA “dog tag”
• Domestic Species ID
• Forensic cases
– matching suspect with evidence
• Convicted felon DNA databases
Steps in DNA Processing
• Sample obtained
– Crime scene or sample
• DNA Extraction
– Removed DNA from cells
• DNA Quantification
– How much DNA is present
• DNA Analysis
– PCR
– Addition of dyes or probes
• DNA Separation & Detection
• Analysis of genomic results
PCR
• Polymerase
Chain
Reaction
• Allows for
exponential
copies of
DNA
• Developed
by Dr. Kary
Mullis (a GT
grad)
Since we are all human. . .
• Most of our DNA is
alike
• Non-coding regions
– Not coding for genes
– Unique
– Certain areas of
genome selected called
loci
• Combinations of loci
selected
DNA Separation
• Separate DNA based on size of fragment
• Detection using probes or dyes
• Common analytical schemes
– Gel electrophoresis
– Capillary electrophoresis
– Future technology
• Polymers
• Micro chips
Gel Electrophoresis
Capillary Electrophoresis
Is it a match?
• DNA isn’t reported as “matching”
– A sample is included or excluded as a possible donor
• Exclusions are relatively straightforward
– genetic marker could not have originated from a
specific individual, that individual is excluded as the
donor
• Inclusion can be far less exact
– An individual may be included among those who
could have generated evidence, but that can be from
one to millions or billions of people
CODIS
• Combined DNA Index
System
– 7,434,897 offender profiles
– 285,425 forensic profiles
• Local, State, National
Levels
– Similar to AFIS
• Compares DNA at 13 loci
– The odds of 2 unrelated
individuals matching at all
13 loci < 1 in 100 trillion
– The earth’s human
population is about 6 billion
DNA v mtDNA
• Nuclear DNA
– Unique
– Found in nucleus of cells
• Mitochondrial DNA
– Passed by mother
– Used if necessary
– Found in bones, hair; places where DNA is
degraded or not present