You cut dna with restirction enzyme and want to see what fragments u get. They way you resolve dna is to resolve based on size. All dna have very similar mass to hcarge ratio. Way most dna differ is in their length. Separation of dna molecules is most esasily done on the basis of length ( # of base pairs). If two dna is same size, its hard to separate. Mass to charge ratio is much the same for all dna but length is diff if two dna have two exact size, its hard to separate. Dna is negative at neutral ph due to phos back bone (-ve) so it will move toward. Gel electrophoresis: way for ppl to most comonly separate dna. For gel eelectrophoresis dna is sieved through a matrix of agarose or acrylamide which contains minute pores. Force supplied to dna is electric field put gel in electric field and electric field will cause dna to move.