DNA profiling

• Genome= all of the genetic material an organism contains.
• Introns= large non-coding regions of DNA.
• DNA profiling= producing an image of patterns in the DNA of an individual.

  • A unique pattern produced by your DNA.
  • Non-coding DNA is used.
• Satellite DNA

  • Mini satellite= sequence of 20-50 base pairs, variable tandem repeats (VNTR)
  • Micro satellite= sequence of 2-4 base pairs, short tandem repeats.
  • Occur at same place on specific chromosome number, but repeated a different number of times.
  • Inherited from parents, so every individual has a different length of repeats.
  • To establish evolutionary relationships, indicators of disease, crime scenes.
• Producing a DNA profile

  1. Extracting the DNA
  2. Digesting the sample
  3. Separating DNA fragments
  4. Hybridisation
• 1. Extracting the DNA  

  • DNA must be extracted using the polymerase chain reacting (PCR machine)
• 2. Digesting the sample

  • The strands of DNA are cut into small fragments using restriction endonucleases.
  • Cut DNA strands at defined points in introns.
  • They use a mixture of restriction enzymes that leave repeating units of satellites intact.
• 3. Separating DNA fragments

  • Cut fragments of DNA need to be separated to form clear and recognisable patterns, using electrophoresis.
• Gel electrophoresis

  1. DNA is negatively charged due to phosphate group.
  2. Fragments are loaded into wells on one end of agarose gel.
  3. Gel is bathed in electrolyte to conduct electricity.
  4. DNA fragments move to positive anode.
  5. The DNA with fewer repeats has less mass so travels through tiny pores in gel more quickly towards the anode.
  6. DNA fragments are transferred to nylon membrane during southern blotting process.
• 4. Hybridisation

  • Radioactive or fluorescent DNA probes are added to DNA fragments. They bind to complementary strands of DNA under certain pH and temperature conditions.
  • Nylon sheet with radioactively labelled DNA fragments is placed into an X-ray film.
  • Reveals where the radioactive DNA probes have attached.
• Probes= single stranded DNA sequences that are complementary to the VNTR regions.

  • Contains a radioactive label or fluorescent dye.
• Polymerase chain reaction

  = To increases the size of the sample, amplify DNA using a PCR machine.

  1. Separating strands= temperature is 95 so denatures the DNA by breaking the hydrogen bonds holding the DNA strands together so they separate.
  2. Annealing of primers= temperature is 55 and the primers bind to the ends of the DNA strands.
  3. Synthesis of DNA= temperature is 72, the optimum temp for DNA polymerase to add bases to the primer, building a complementary strands of DNA identical to original sequence.