Gels, such as polyacrylamide gels, are provided that include linear polyacrylamide in the stacking gel. Native gels that include linear polyacrylamide in the stacker can be used to separate biomolecular complexes, such as protein complexes. Gel cassettes in which the gap width between front and back plates does not vary by more than 5% at the upper edge of the cassette are also provided. The gel cassettes can be used for electrophoretic separation of proteins and protein complexes on native gels, such as native gels that include linear polyacrylamide in the stacker. The native gels can have multiple wells for electrophoresing at least one sample and/or at least one molecular weight standard.