Steps involved in determining the DNA sequence of a sample.

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lynn30k eNotes educator| Certified Educator

DNA sequencing refers to determining the order of nitrogenous bases (adenine, guanine, thymine, and cytosine) in a piece of genetic material. In modern methods much of the work is automated but the steps remain the same.

  1. DNA is extracted from cells. This is easy to do, and many high school biology classes extract the DNA from fruit such as strawberries using only dish soap, cold alcohol, and a baggie.
  2. Polymerase chain reaction (PCR) is performed on the sample in order to multiply the number of copies of the DNA. The helix is opened and copied multiple times.
  3. The DNA sample is run through gel electrophoresis. DNA has an overall negative charge. The sample is placed at one end of a gel, and electric current is run though so that the sample is attracted to the opposite, positive end of the apparatus. Because the smaller fragments of DNA travel more quickly through the gel, bands form that have the smaller fragments closest to the positive end, and the larger fragments stay closer to the origin; they take longer to travel through the gel.
  4. The resulting band patterns are decoded by an automated sequencer, which "reads" the nitrogenous base sequence.

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