Electrophoresis (Unit 4, Topic 6 Core Practical)

Step by step on how to carry out electrophoresis and how we derive DNA profiles from it.

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DNA Preparation

  • DNA is cut into fragments by restriction endonuclease
    => the enzyme cuts at specific points called recognition sites
    => fragments are a mixture of mini-satellite and micro-satellite sequences
  • DNA fragments are placed into the wells of an agarose gel
    => the gel contains a dye that binds to the DNA 
    => this becomes flurescent under Ultraviolet light and the DNA fragments become visible
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Movement of the fragments

  • An electrical current is passed through the agarose plate
    => this runs through the DNA fragments and makes them move across the agarose plate
  • DNA fragments more towards the positive anode
    => this is because of the negative charge on the phosphate group of the DNA 
    => the lighter/smaller fragments will move quicker
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Result

  • Electric current is turned off to observe the DNA fragments
    => UV light is shone onto the fragments to make them visible
    => this creates the DNA profile 
  • The location of the fragments then can be matched up to another DNA profile, and where the locations show up the same 
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