Gob-smacked

A few burbles ago, I mentioned that I’d be reporting back on my Year 10 Biotechnology Club, and how they had fared in their attempts to work out Mendelian laws of inheritance from first principle. I hadn’t seen them for a couple of weeks because of various other commitments, but now I have. And, well, wow.

So, just to recap, this is what they did.

I got in some flies. Fruit flies. This is the place: http://blades-bio.co.uk/

We already use Drosophila in Year 13 to investigate sex linkage, but I thought it would be worth trying them on a talented and motivated bunch of Year 10s to look at basic autosomal inheritance. I was initially just going to get some vestigial winged flies and cross them with wild types, but looking at the catalogue I started to see the possibilities, and ended up ordering vestigial winged males and females, and ebony males and females. Then I got the girls to set up vestigial/ebony crosses.

You can’t really go wrong with this as an activity. It’s just brilliant fun – different, interesting, challenging, in every way.  Knocking out the flies, setting up the little breeding tubes, making sure the unconscious flies don’t get stuck in the blue food goo or get smeared across the sorting paper by heavy handed use of a paintbrush, checking the flies have come round, looking first for larvae and the little tunnels through the food, and then for pupae, and then finally for the alarming clouds of offspring…

But the excitement really starts when they knock them out again and look at the phenotypes.

Remember, these are students who haven’t done any genetics. So there’s no pre-conceived theory or received ideas to help them explain or predict. They just see for themselves, from their own crosses, that ebony bodies and vestigial wings have disappeared. Vanished. Every single one of those first generation flies are 100% wild-type.

It’s the kind of thrill that Mendel himself must have had when the pea dwarfiness disappeared. That’s funny…. what’s going on?

And so they cross the first generation flies. This raises the skill bar considerably, as they have to distinguish males from females based on a tiny little black bristle on their front legs.

Slightly stressful, too, as they don’t give them quite enough ether and are still trying to identify males under the binocular microscopes when the knocked out flies start their little break dances, and then start to escape…. It’s a race to set up the new tubes and fly mortality is high…

But a couple of tubes are successful, which was probably a good thing because there are LOTS of F2 generation offspring to count. The students are brilliant, sharing out the work, and dutifully tallying up the 4 different phenotypes. Because, lo and behold, ebony and vestigial is back. In the rather wonderfully perfect ratios of 95 normal wing, normal body, 34 normal winged ebony body, 24 vestigial winged normal body, and 5 of the fly they’ve not yet seen, those with vestigial wings and ebony bodies.

Go on, I say, work it out.

They’re good. Oh, golly, they’re good. By the end of the session, working together, with absolutely no input from me whatsoever, they report that the expected ratio should be 9:3:3:1

I’ll admit it, I’m shocked. I thought they might get the basic idea of dominant and recessive alleles and how a characteristic could disappear for a generation. I thought they might even figure out the ratio of a simple monohybrid cross. But they’ve only gone and worked out the predicted ratio of a dihybrid cross. And seen that their results closely matches their prediction.

Make your students feel brilliant and they will do brilliant things.

I’m now wondering whether we could roll this out as an investigation for the Year 11s when they actually do genetics in the SoW. Cost is a consideration – virgin females are not cheap – and you’d have to be very tight on health and safety – ether is nasty stuff – but it’s got to be more interesting than pea plants….

Go to run. OCR moderation sample request has just come in…

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