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DNA Forensic Identification Ashley Kowaleski I400 Objectives 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?

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dna forensic identification

DNA Forensic Identification

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 involve?
  • How are criminals processed?
  • What is the outlook for the future?
forensic science
Forensic Science
  • Process of gathering and examining evidence of a crime
  • First practiced forensic medicine in 1958
  • Italy
  • Application of medical knowledge to legal questions
unique identifiers

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 science

Unique Identifiers
dna deoxyribonucleic acid
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 person
dna identification
DNA Identification
  • Uses
    • Investigations of criminal cases involving victims
      • Assault
      • Kidnapping
      • Robbery
      • Rape
      • Murder
    • Catastrophe victims
    • Paternity/family relationships
    • Identify endangered and protected species
    • Detect bacteria/organisms that may pollute the air, water, food, and soil
    • Match organ donors with recipients
    • Determine pedigree for seed/livestock breeds
    • Authenticate consumables such as caviar and wine
short tandem repeats str
Short Tandem Repeats (STR)
  • STR regions are nucleotides along the backbone of a chromosome
  • 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
The Process
  • Isolation
  • Quantifying
  • 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 repeated
  • 1-2 hours
polymerase chain reaction pcr
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 pcr13
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 nucleotides
  • Repeated rapidly, doubling amount of DNA
str pcr
  • 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 ce
Capillary Electrophoresis (CE)
  • 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 makeup
  • This is the information used to compare suspects to a crime
  • http://chemi.muni.cz/~analytika/ce/ce-animation.gif
  • 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 codis
National DNA Databank: CODIS
  • 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
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