Time for another reflection on my mundane week of teaching. I know this is unexciting, but I’m trying to be self-aware about what I’m doing in the class.
I’ve already summarized some of what I did this week: we explored the meaning of “epigenetics”, and I made a big push to get them to think critically about the papers we’re reading. They’re supposed to be developing a topic they’ll explore independently, so I’ve had them doing library work to find a line of research they find interesting, and master the skill of extracting the key questions the work is trying to address. I’ve got a small stack of short papers that I’m going to read this weekend and we’ll see how well they can do that.
We also discussed symbiotic interactions in development, and next week the topic is other environmental effects. They are getting much, much better at opening up and talking at the miserable hour of 8am.
The other regular highlight of my week is FlyDay, when I have to scrub dead maggots and pupae out of fly bottles. I had to postpone FlyDay this week! Yesterday I was scheduled to meet with students and parents visiting the university to confirm their plans to attend, and I was all spiffed up in a nice suit, which isn’t the best thing to wear when one is flicking bits of chitin and gooey medium around. I went in early this morning to scrub bottles and get them cooking in the autoclave.
By the way, at that student meeting I was the official biology representative, and although biology is currently the largest major on campus, almost no one stopped by to talk to me. It might have been my terrifying glare, or my sciencey reek, but no: it was because there was a separate table for the pre-professional programs (pre-med, pre-vet, pre-dental, etc.). This is a minor peeve of mine: this is not 19th century England. You do not graduate from your public school education and go straight into medical school — no, here in 21st century America you get a broad-based undergraduate education first, and then you apply to med school. You should be thinking about your liberal arts education first, and in a couple of years we’ll start coaching you on how to get into those professional programs.
Oh, well. They ignore me now, but I know that I’ll get my claws on most of them soon — they’ll want all those bio classes to prep them for the MCATs.
I should mention that I am teaching another course beyond ecological development — I’m teaching a lab course on transmission genetics. They’ve been doing crosses with flies all semester long, and we’re getting to an interesting point.
The first half semester we’re doing a mapping cross, using recombination to estimate the distances between a couple of genes on the X chromosome. We’re using flies that are mutant for eye color (white, w), wing length (miniature, m), and bristle morphology (forked, f), and I’ve also got a few groups mapping body color (yellow, y), wing veins (crossveinless, cv) and forked, f; the latter are doing a pilot test to see if I want to add that cross to our regular repertoire.
The way this works is that they are given wild type and triple mutant flies. I first have them raise a new generation of the purebred stock, simply to get a little practice in sexing flies and basic skills in growing them. So they first do these crosses:
♀w– m– f–/w– m– f– x ♂w– m– f–/Y
which produces bottles full of homozygous white-eyed, miniature-winged, forked-bristled flies, and
♀w+ m+ f+/w+ m+ f+ x ♂w+ m+ f+/Y
which produces bottles full of homozygous wild type flies.
Then I have them do a reciprocal cross of flies from the two bottles. These are X-linked traits, so it matters which strain is the mother and which the father, and I want them to see that. That is, they cross wild type females to triple mutant males, like so:
♀w+ m+ f+/w+ m+ f+ x ♂w– m– f–/Y,
which produces progeny that are all wild type, both male and female (they all inherit the dominant wild type allele at all loci from their mothers). After they’ve scored the flies from this cross, we dispose of them all and don’t think any further about them.
They also cross mutant females to wild type males, like this:
♀w– m– f–/w– m– f– x ♂w+ m+ f+/Y.
That has the useful result that all the sons inherit w– m– f– from their mother and a Y chromosome from their father, so they all express the mutant phenotype. The daughters, however, are all heterozygous, inheriting the mutant alleles from their mother and a wild type chromosome from their father, so their genotype is:
♀w– m– f–/w+ m+ f+
Now the fun begins. Meiotic recombination in those flies will rearrange the +’s and -‘s in those chromosomes with a frequency dependent on their distance from one another — you’ll get less recombination between genes that are close to one another.
This week, they completed the reciprocal cross and got their heterozygous females and mutant males. Yay! That worked. They are now setting up a test cross to assess recombination frequencies.
I just want to say that I think I planned everything perfectly. That test cross will be ready to score next week, which is the week before spring break, which means we’ll have the data for all the calculations before they leave, and when they get back, I’ll be able to lead them through all the theory. It also means I’ll be able to purge a lot of fly bottles and get them scrubbed up over the break (you can tell already that I have glamorous plans for my short vacation). Trust me, though, this is good — there have been semesters where, due to student error, the flies haven’t been ready, and then my spring break is spent maintaining 120 bottles of student flies.
It also means we can launch into the next experiment as soon as they get back: we’re going to do a complementation cross between two eye color mutants, brown eye (bw) and scarlet eye (st). If I’ve got this one all timed out correctly, we’ll be getting F2 results of crosses between heterozygotes for both loci a week before the end of classes.
Now you know. I choreograph fly sex for my convenience.
Next up, I have to choreograph my schedule. It turns out I have been summoned to Howard Hughes headquarters on 8 March and 18 April, which punch big holes in my planned lessons, and which I hadn’t accounted for in my syllabi. I’m going to have to juggle lectures and exams and rearrange the order of various things in a big way this coming week.