The limitations of standard gel ele

The limitations of standard gel electrophoresis can be overcome if a more com￾plex electric field is used. Although several different systems have been designed,the principle is best illustrated by orthogonal field alternation gel electrophoresis(OFAGE). Instead of being applied directly along the length of the gel (as in the stan￾dard method; Figure 4.18a), the electric field now alternates between two pairs ofelectrodes, each pair set at an angle of 45◦ to the length of the gel (Figure 4.18b).The result is a pulsed electric field, with the DNA molecules in the gel having con￾tinually to change direction in accordance with the pulses. As the two fields alter￾nate in a regular fashion, the net movement of the DNA molecules in the gel is