There is a specific density of gel used in the electrophoresis.The DNA is placed in a well, and then electrical charge is used topull the DNA through the gel. Because spliced DNA is slightlycharged, it begins to move through the gel. The density of the gelcauses the larger pieces to go slower than the smaller pieces.Think of it like this: what is a faster way to get through rushhour traffic? Using a bicycle to pedal through all the cars, orbeing stuck in a taxi cab. The taxi cab, which is larger, movesslower through the traffic. The bicycle which is smaller, movesquicker.