Teaching Notes from Amy Bejsovec

I use shits and wg1 flies in my introductory genetics class to demonstrate basic principles about mutations.  These stocks can be used in large lecture formats since they show dramatic adult phenotypes.  Flies can be put into a large Petri dish with a moist wad of Kimwipe to keep them hydrated, and the dish can be put directly onto an overhead projector to project the silhouettes of the flies. 

I use shits to demonstrate temperature sensitivity of certain missense mutations.  This works best with a Petri dish of wild-type flies to compare with a dish of  shits homozygous flies.  Both are fine at room temperature and the flies will run around actively in the dishes when you project them onto the overhead screen.  I then ask a student to put one dish under each arm to warm them up to body temperature.  This knocks out the shi flies within a minute or two, but doesn't bother the wild-type flies at all.  When you retrieve the dishes and put them back on the overhead projector, the shits flies are paralyzed.  If you can resist making jokes about "toxic arm pit odor", this is a great demonstration of the missense change in dynamin (the protein that shibire encodes), which renders it inactive at high temperatures and blocks endocytosis so that membrane recycling at the synapse shuts down.  The flies will recover more quickly if you take them off the projector, which tends to be too warm.  Usually they are back up and running around within a few minutes.

I use the wingless flies to demonstrate genes that pattern the body, and the projection of wg1flies next to a dish of wild-type flies is quite striking.  I have also used these flies to test the students' powers of observation.  Every year when I do my lecture on X-linked inheritance, I pass around sets of Petri dishes (lids firmly taped on!) - one with white-eyed flies and one with wild-type red-eyed flies so that students can see the mutant phenotypes I'm describing in my lecture.  This year, I "spiked" the dishes with a few wg1flies mixed in with the normal-winged flies.  The original wgstock has white eyes because they are doubly mutant for cn and bw; and I've generated a stock that only carries the cn mutation, so their eyes look similar to wild-type.  I've also bred both lines to increase the penetrance of the completely wingless phenotype.  When I started passing around the dishes, I told the students that they should look carefully at the eye colors but also be on the look-out for anything else unusual because I was playing a little trick on them.  This definitely got their attention!  At the end of class I quizzed them to see how many had managed to spot the wingless flies.  This provided a nice opportunity to talk about how all good science starts with careful observation, and to talk about our Biology Dept.'s independent study program to get them thinking about doing science in a real research laboratory.  Certainly the ones who spotted the wingless flies were good candidates for helping out with genetic screens in my lab!

Amy Bejsovec, Ph.D.
Duke University