The method of gel electrophoresis was developed in the 1970s to separate fragments of DNA as they migrate through a gel, a porous sponge-like medium. An electric current pulls smaller molecules faster than larger ones. When the molecules are closed loops of DNA, biologists believe that the motion is determined by the "average crossing number". However other knot invariants may be relevant to such motion. We define and compute some of these, and relate them to other knot invariants. This is joint work with Hyam Rubinstein and Abigail Thompson. ---------