Blotting

The DNA is first transferred from the gel to a membrane by capillary action. Fluid wicks from the gel through the blotting membrane to several layers of absorbent paper, but the nucleic acids stick to the membrane. Baking the filter fixes the DNA or RNA to the filter.

Specific bands are detected by hybridization. The filter membrane is incubated with radioactive probe, which hybridizes to some bands. After the filter is washed (to remove unused probe), an X-ray film exposed to the filter will show which bands have hybridized.