“Scientists knew that they could chop up DNA using restriction enzymes... They could then
separate the resulting pieces by loading the collection onto an agarose gel and applying an
electric current. The pieces would migrate at different rates, depending on size… For
organisms with large genomes, however, this procedure generated a smear of DNA…
Finding a single piece of DNA that carried a specific sequence was hopeless… Southern
realized that he could accomplish his task by brute force: carving the gel into small …