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Reading a DNA sequence

Once scientists have made many partial copies of the DNA they use an electric field to separate them by passing them through a gel, a thin jelly-like slab. The shorter the piece, the faster it travels. They tag the pieces of DNA with a radioactive chemical, so they can see their final position in the gel. The pieces in the gel are arranged according to their size, which shows the order of the letters in the DNA strand.

The second part of DNA sequencing.

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