I know many upper-level biology classes perform some version of the classic (are they old enough to be classic yet?) biotechnology procedures at some point in the year. Bacterial transformation, PCR, and DNA electrophoresis are all experiments that occur in many labs at high schools and universities. I say occur but what I mean is attempt. At least in my classroom the success rate for these procedures is… let’s say <100%.
Practice makes improvement but in this setting practice is also really expensive. To solve this problem my predecessor (the venerable Paula Donham to cite her properly) allowed students to practice some procedures on dummy supplies first before using actual reagents and equipment. This is particularly useful in electrophoresis procedures. Micropipetting is difficult to novices and errors can ‘break’ the experiment with discouraging frequency. This is a particular problem in experiments that are culminating in the electrophoresis step after substantial investment, such as the arabidopsis epigenetics lab that I’ve raved about before.
A practice gel can be cast in a Petri dish with the much cheaper agar (as opposed to agarose) and water. Mix a 1% agar solution with tap water and boil to dissolve. Pour molten agar into Petri dishes to a depth of about 5mm. While it is still molten add a comb that creates several rows of wells similar to those in an electrophoresis gel. After the agar solidifies fill the dish with water. Use glycerol with food coloring to practice filling the wells with no harm from gel punctures, spills or other experimenter errors.
Usually you could buy equipment or kits (like here) but there is a DIY option. You can mix your own reagents as I’ve described above and you can 3D print your own comb. Download the STL file here and get your nearest 3D printer to create you an army of combs. Now every student can practice melting, pouring, comb-removing, and loading. This time your students can make much more interesting mistakes than simply misloading their wells.