Agarose Gel Electrophoresis is a technique used in genetic screening to determine whether a gene is present or not.
First the DNA is cut using a restriction enzyme. These recognise specific sequences of DNA and make an incision if they find it. If the sequence isn't present, the enzyme will not cut.
The electrophoresis chamber runs from negative to positive and because DNA has a slight negative charge it will be drawn to the positive end.
DNA is separated on the basis of size, smaller fragments running faster.
If a gene is present a probe is inserted that recognises and binds to the sequence. This is how CF is screened for.
Note: The electrophoresis practical (activity 2.19) is a core practical and all questions must be answered.
Links:
University of Utah virtual lab
Colorado state university
Gene almanac animation