This difference makes it possible to cleave a long dna molecule into the fragment sizes that are most suitable: many sites of cleavage occur purely by chance in any long. After the cleavage, the dna fragments are separated from one another on the basis of their length by gel electrophoresis: mixture of dna fragments is loaded to one end of an agarose gel. The gel contains a microscopic network of pores. High voltage is applied across the gel and the negatively charged dna fragments migrate towards the positive electrode. - the larger the fragment, the longer it takes. The dna can then be excised and extracted. Hybridization provides a sensitive way to detect specific nucleotide sequences: Design a short, single stranded dna probe that is complementary to the nucleotide sequence of interest. Can use the probe to find a sequence among the dna fragments that have been separated on an agarose gel.