Day 33: What Kills the Flies?

BACK!

Thanks to the Polar Vortex my flies got some extra hibernation time, but we brought them back out into the world today!

Luckily, mostly all of the culture tubes had viable offspring (minus the pink ones with strep – Awesome yet kind of scary to find in your fly cultures).

Today, I asked students to recall what the stages of the Drosophila life cycle are, how long each stage lasts, as well as the anatomical positions on the fly. For the most part, the remembered, it was the simplest way to see what they recalled of the basic terminology over break.

Then students in their pairs were asked to put their flies to sleep using FlyNap* and then count the ratio of orange-eyed, curly-winged to white-eyed, straight-winged individuals. The catch? There should have been ZERO straight-winged organisms. Why? Let’s refresh:

We crossed Tep3/cyoYFP x Tep3/cyoYFP in December, and our expected outcomes are  25% Tep3/Tep3, 50% Tep3/cyoYFP, or 25% cyoYFP/cyoYFP. We know that Tep3/cyoYFP have orange eyes and curly wings so 50% of our offspring should be curly-winged and orange-eyed. But what about the others? Turns out because the cyoYFP gene is on a balancer chromosome which means it can’t be inherited with another balancer chromosome or it’s lethal. So 25% don’t make it as embryos. But the other 25%? The Tep3/Tep3? Well, that’s our question, all we know logically is that they WON’T have orange eyes or curly wings. So if we see non-orange-eyed, curly-winged individuals, then we know the Tep3/Tep3 flies don’t live to adulthood. *DRUMROLL*

100% orange-eyed, curly-winged…“Hmmmm…”, my clever students say.

Interestingly, by telling students to look for orange-eyed flies or white-eyed flies (without connecting the dots for them like I did above) some students are tricked into thinking they must have SOME white flies. Mostly, we checked out these supposed “non-orange-eyed” flies and they always turned out to be orange-eyed. An interesting form of introducing bias, although only in the freshman, none of my AP students took the bait. Students then inputed their data into a Google Spreadsheet with their data. In AP, I asked a student to create their own spreadsheet and then share it with the rest of the class, I didn’t give them this.

After that, the freshman transfered their adults to a new culture tube, UNLESS they asked a super research question. See we told students to listen to themselves and any question that popped up, which they should record and share with us. Normally, students see no incentive to do this, outside of their own curiosity. But there were so many dead pupa in their vials that is led to some questions like, “Why are they dying?”, “When are they dying?”, “Are they malnourished?”, “What are mostly pupa dying?” or my favorite:

Ah! But those are not the normal culture tubes; they are urine-sample cups.** Students with fleshed-out questions and ways to investigate those were given a cup and an apple-juice agar plate to put their flies in…and that about provided all the jealousy needed to trigger a storm of questioning. “Why do they get a cup for their flies?!” “How do I get one?!” My response, “Well, do you have any good questions?” It seems the only thing needed to get students to take this seriously was some students getting something the others didn’t. No grades or extra credit. Not even a Jolly Rancher.

So how many good questions did I get from 130 students?

So now with these cups, student pairs who didn’t have well-developed questions will now choose questions other students asked. So they still get a choice with what interests them and they’ll have more chances to ask questions that move them in new directions, but for now, we have an incubator full of initial questions. My AP students each got an apple-juice plate and cup themselves and will each be able to lead their own investigations.

Next time (Monday): Students will choose a question and begin observing the young growing on the new agar plates.

* Side-note: I’m not crazy about this method. It’s messy, it smells, it requires constant resetting by dipping the wands in FlyNap every hour. I know professional labs used CO2 and I’ve heard of some alternatives such as alka seltzer or other smaller CO2 sources. (SodaStream!?)

**DO NOT TELL STUDENTS THIS (or prepare for epic levels of gross-out)