Southern Hospitality...

When the samples have run far enough down the gel to provide a good separation, a picture is taken of the gel by placing it on a lightbox. As you can see, the areas on the gel where the DNA has migrated light up, showing the pattern of the sample. Now the DNA is transferred from the gel to a nylon support, like this white membrane, and crosslinked to hold the DNA in place. Before the transfer, the DNA is denatured in the gel to separate the stands of the double helix.

The transfer process is known as a Southern blot, named after the scientist who invented the procedure. A Southern blot is when DNA is immobilized on the membrane *and* DNA is used as a probe. Now caution needs to be taken. The probe we will generate will be radioactive. DNA is made of nucleotides and we will incorportate some radioactive ones into a strand of DNA to make it "hot". This probe is then boiled to separate the two strands and now the single strand of the probe can anneal to the single stranded DNA on the nylon.

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