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a technique used to separate pieces of DNA by length using electricity to entice the (naturally negatively-charged) DNA through a slab of gel made of the sugar agarose towards a positive charge. The DNA strands get tangled up in the mesh as they go (kinda like if you were to try to pull jumpropes through a sea of basketball hoops), and this slows them down. The longer the DNA, the more it gets tangled up, so the slower it travels and thus, when you turn off the electricity, longer DNA pieces will be closer to the starting end of the gel and smaller pieces will be further away. You can use a fluorescent DNA-binding stain to visualize where the DNA pieces end up (they’ll appear as bands). Unlike SDS-PAGE, which we use to separate proteins by size, agarose gel electrophoresis is typically done in a horizontal format. You can adjust the % of agarose you use to get tighter or looser meshes depending on the size of the DNA pieces you want to resolve (be able to tell apart).