DNA profile

• How do we obtain DNA sample?

  • Extract from cells
• How do we amplify DNA?

  PCR
• Describe PCR


  95°C - Denaturation:

  • DNA splits into 2 strands
  • H bonds between bases break

  55°C - Annealing:

  • Primers attach to start of STR sequence

  72°C - Extension:

  • Taq DNA polymerase (thermostable) binds to DNA strand where primer is attached
  • Synthesises a new complementary strand of DNA
• What do you do with the amplified DNA?

  • Cut DNA into fragments (cut out STR sequences)
  • Using restriction endonuclease
• What do you do with the fragments of DNA?

  • Seperate using gel electrophoresis
• How are DNA profiles compared?

  • Compare total no. of bands
  • Compare position of bands
  • Compare size/width of bands
• Is DNA profiling reliable?

  Yes-

  • Everyones DNA is unique

  No -

  • Multistep process - contamination
  • Identical twins have identical DNA profiles
  • Close relatives have similar DNA profiles
  • If only analyse a few STR - less reliable