Gel electrophresis

• Genetic fingerprinting


  Examination of VNTRs (variable number tandem repeats) in the introns of human DNA
• 95% or more of human DNA are introns (non-coding regions)
• VNTRs


  Long sequences of DNA bases that repeat over and over, but don't code for anything
• The probability of two individuals having the same VNTRs is incredibly low
• The more closely related you are to someone, the more similar their VNTRs are
• Genetic fingerprinting process


  1. Collection and extraction

  2. Digestion

  3. Separation (gel electrophoresis)

  4. Hybridization

  5. Development

  6. Analysis
• Restriction endonucleases


  Enzymes that cut DNA just before and after VNTRs
• Gel electrophoresis


  1. DNA samples pipetted into wells in agar gel

  2. Electrical voltage applied, causing negatively charged DNA to move towards positive end

  3. Smaller VNTRs move faster through gel
• DNA probes


  Short, single-stranded pieces of DNA designed to be complementary to VNTRs, and labelled with radioactive or fluorescent chemicals
• Developing the gel


  1. DNA with attached probes transferred to nylon sheet

  2. Exposed to X-rays (radioactive probes) or UV light (fluorescent probes) to visualise VNTRs
• Marker


  DNA sample with VNTRs of known lengths, used as a reference
• Applications of genetic fingerprinting

  • Forensic science (placing suspects at crime scenes)
  • Paternity testing
  • Medical diagnosis
  • Animal and plant breeding programs
• Genetic fingerprinting is used to reduce the risk of passing on harmful genetic conditions