Abstract: An electrophoresis cassette is made from two substrates separated by spacers, and a one-piece molded plastic edge adapter. The edge adapter provides the contoured edge to facilitate sample loading, and because it is made from molded plastic is easier to make. Furthermore, the edge adapter has vertically extending arms which define the sides of the loading region and which, when glued to the back substrate, prevent leakage of buffer solution from the region surrounding the electrophoresis origin. In one variation, a groove in the bottom edge of the edge adapter receives the top edge of the front substrate to further define the position of the edge adapter in relation to the substrate. Vertical divider fins may optionally be formed on the contoured surface of the edge adapter. These divider fins define loading wells for the introduction of sample into the lanes of the electrophoresis gel.