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DNA Forensic
Ashley Kowaleski
What is forensic science?
How and when did forensics begin?
When was DNA identification discovered?
What is DNA identification used to determine?
What exactly are forensic scientist looking for?
What is the process does DNA identification
 How are criminals processed?
 What is the outlook for the future?
Forensic Science
 Process of gathering and examining
evidence of a crime
 First practiced forensic medicine in 1958
 Italy
 Application of medical knowledge to legal
Unique Identifiers
 Fingerprints
 When a persons hand
touched a surface, it left a
barely visible mark
 Each person’s fingerprint
is a unique identifier of
that person, no two
people’s are alike
 Genetic material that is
found in DNA is also a
unique identifier
 Not until1985 when DNA
became part of forensic
DNA (deoxyribonucleic acid)
 Nucleic acid that carries the genetic information
 Double helix
 2 long chains of nucleotides twisted and joined
by hydrogen bonds
 Can be found in white blood cells
 Polymorphic: vary in shape from person to
DNA Identification
 Uses
 Investigations of criminal cases involving victims
Catastrophe victims
Paternity/family relationships
Identify endangered and protected species
Detect bacteria/organisms that may pollute the air, water, food, and
 Match organ donors with recipients
 Determine pedigree for seed/livestock breeds
 Authenticate consumables such as caviar and wine
Short Tandem Repeats
 STR regions are nucleotides along the backbone of a
 13 markers used in forensic science
 Classified into groups depending on the size of the
repeat regions
 Mini satellites
 Micro satellites
 The chance that any two peoples DNA fingerprint for a
particular set of regions is exceptionally small
 1/10th of a single % of DNA, about 3 million bp, differ from one
person to the next
The Process
Polymerase Chain Reaction (PCR)
Short Tandem Repeat-Polymerase Chain
Reaction (STR-PCR)
 Interpretation
 Database
 Scientist extract DNA from the nucleus of
cells in tissue
 Quality of tissue DNA samples degrades
as body decomposes
 1-4 hours
 Tests are run to determine the amount of
DNA recovered
 Targeted amount 1 nanogram (billionth of
a gram)
 If inadequate quantity, isolation must be
 1-2 hours
Polymerase Chain
Reaction (PCR)
 One of the most popular and widely used
techniques in molecular biology
 Reproduces millions of exact copies of
specific fragments of DNA
 Enables even highly degraded samples
to be analyzed
 3 hours
Polymerase Chain Reaction
Polymerase Chain
Reaction (PCR)
Based on polymerase enzyme
Break apart double helix, two single strands
Rebuild two strands into two complete helixes
DNA deposited into polymerases and
 Repeated rapidly, doubling amount of DNA
 Mainly same process
 Focus solely on STR regions
 Since these repeat regions are usually
bounded by specific restriction enzyme
sites, it is possible to cut out the segment
of the chromosome
Capillary Electrophoresis
 Early 1990’s
 Automated analytical technique
 Generally used for separating ions, which move at
different speeds when the voltage is applied depending
on their size and charge. The solutes are seen as
peaks as they pass through the detector
 Area of each peak is proportional to their concentration
 Produces a chart mapping a person’s exact genetic
 This is the information used to compare suspects to a
Capillary Electrophoresis
 A DNA scientist reviews the DNA profile
produced through the capillary electrophoresis
to determine if there is a match
 STR markers are examined (2-5 bp)
 1-3 are not enough to determine is the sample
came from the suspect
 4-5, beyond a reasonable doubt
 5 very rare
National DNA Databank:
 The COmbined DNA Index System
 Blends computer and DNA technologies into a
tool for fighting crime
 2 indexes
 Convicted Offender Index
 DNA profiles of individuals convicted of criminal crimes
 Forensic Index
 DNA profiles developed from crime scene evidence
 All profiles stored in CODIS are generated
using STR analysis
The Future
 March 2004: President Bush proposed
$1 billion in funding over the next 5 years
Reduce DNA testing backlog
Build crime lab capacity
Stimulate research and development
Support training
Protect the innocent
Identify missing persons