DNA Analysis Techniques

• Polymerase Chain Reaction (PCR)



  PCR is a technique used to amplify specific DNA sequences. It involves:

  1. Primers
  2. Temperature Changes
  3. Taq Polymerase
• Primers: 


  Short DNA sequences that bind to the target DNA and provide a starting point for replication.
• Temperature Changes:

  The PCR process involves cycles of temperature changes:

  • Denaturation (94-96°C): Separates DNA strands
  • Annealing (50-65°C): Allows primers to bind
  • Extension (72°C): DNA polymerase synthesizes new strands
• Taq Polymerase


  A heat-stable DNA polymerase from the bacterium Thermus aquaticus, which can withstand the high temperatures in PCR.
• Gel Electrophoresis


  Gel electrophoresis is used to separate DNA fragments based on size:

  1. Principle: Negatively charged DNA molecules move through a gel towards the positive electrode when an electric field is applied.
  2. Separation: Smaller fragments move faster through the gel pores than larger ones.
• PCR and Gel Electrophoresis


  These techniques have revolutionized molecular biology and have a wide range of applications:

  1. DNA Profiling
  2. Medical Applications
  3. Research Applications
  4. Environmental Applications
• DNA Profiling


  • Forensic Investigations: Analyzing DNA evidence from crime scenes.
  • Paternity Testing: Determining biological relationships.
• Medical Applications


  • Genetic Disease Diagnosis: Identifying genetic mutations.
  • Cancer Detection: Analyzing tumor-specific genetic markers.
• Practical Considerations:

  • CODIS (Combined DNA Index System) used by the FBI initially used 13 core loci (markers), but has expanded to 20 core loci to increase reliability.
  • European Standard Set (ESS) has increased from 7 to 12 loci.
• The expansion of marker sets in DNA profiling systems worldwide reflects the scientific community's commitment to enhancing reliability and reducing the chance of false matches.