If you didn't finish all the analysis of the cat data last week, finish it now. The lab report on the cat data is now due Thursday, Sept. 10.
(This experiment will be done by one or two people who finished the cat data analysis first.) The fly food you made the first day was too dry, despite following the recipe provided with the food (equal volumes of dehydrated food and water). I think the problem is that the food settles with time; as it gets denser, one teaspoon of food would take more than one teaspoon of water to reach the right consistency.
For the rest of the semester, you'll weigh the food, and you'll measure the water in a graduated cylinder. To figure out the correct proportions, weigh two level teaspoons of the dry food. Put this in a vial labelled with the weight of the food. Then make several other labelled vials, and weigh out the food that goes in each one. One vial should get 90% as much food as the first vial; one should get 80% as much; and so on, down to 50% as much food. Add 10 ml of water (carefully measured with the graduated cylinder) to each vial. Let it sit for a few minutes, then ask me to help you decide which is the best.
Look at the vial of flies you set up on Tuesday. By now, the food should be crawling with larvae; you should see their white bodies moving against the side of the vial, buried in the food. If you have plenty of larvae, clean out the old vial that I first gave you (the one with yellowish-brown food, not the blue food that you set up). To clean it out, knock the adult flies through a funnel into a morgue. Then remove the label, rinse the food out, and wash out any stuck-on food and pupal cases with the bottle brush. Soak the foam plug with water and squeeze it out; repeat this several times, and get any stuck on pupal cases off the foam. Put the washed vial and plug in the plastic tub next to the sink.
There's nothing toxic about the fly food, but it's kind of gross; you can get disposable gloves in the lab.
If the vial of flies you set up last week failed (there are no larvae in it), clean out the failed vial, then set up a new one from the original vial. Use the new recipe determined by one of your classmates in the first part of this lab. In this case, do not clean out the original vial until next week.
The mixture of mutant and wild-type flies that you are taking care of was established by mixing one inbred line of wild-type flies and one inbred line of mutant flies. You may need these pure lines for your individual experiment. To keep them going, you and your mutant partner should make a vial of food (using the new recipe), label it, and transfer the adults from the original vial to the new vial. You can then clean out the old vial.
The lab report that is due on Tuesday, Sept. 15, will be a proposal for your individual project. You will look at the literature on your fly mutation, plus the term papers last year's students wrote on the same mutation, and come up with an experiment to investigate any fitness difference between your mutant allele and the wild-type allele. Of course, we don't know for a few weeks whether there is a difference in fitness, but you'll plan your experiment assuming that you'll see something similar to what last year's students saw.
Today you'll research your gene in Flybase, skim through last year's term papers, and obtain the most relevant literature. Because most of you have classic visible mutations that have been known for decades, you may find that there is an overwhelming amount of literature. You don't have to read everything that is known about your gene, but focus on the following questions. You may find much of this information in last year's term papers, but you'll want to double-check the original references when you write your paper.
To start researching your gene, go to FlyBase, a comprehensive database on Drosophila genes, and search for the abbreviation of your gene. The abbreviation is on the original vial you were given ("w", "sd", etc.). Once you find it, click on the link for "alleles" to see a list of known alleles at your gene. Try to figure out which of these alleles is your mutant. Because you have a classic, well-studied mutant, it probably has a low allele number, and a large number of stocks are probably available. I think the superscript number on the original stock ("w1, sd3, etc.) is the allele number, but I'm not sure.
Once you find your allele, record the information described above and the references to important papers where you can look up more details. Note that in the description of the mutant phenotype, there may be a lengthy description of phenotypes of flies that have both your allele and other mutant alleles. You don't need that; just record the description of the phenotype produced by your allele alone.
Next, start reading last year's term papers. Note the important references about laboratory selection experiments. Figure out whether they're available online, available in print in the Morris Library, or not available. If you're not sure how to do this, see the guide to searching literature. If there are some important articles that aren't available in our library, order them through Interlibrary Loan.
A very useful literature tool is Web of Science (go here if you're off campus). If you don't know how to use it, go to the guide to searching literature. Look up the most relevant reference on laboratory selection in Web of Science, then see who has cited it. You may find some important references on your mutant that aren't in last year's term papers (some of last year's students didn't do a very thorough literature search).
The experiment that you'll propose can be the same idea as the one done last year, only improved; the same idea as one in the literature; or something completely new. You and your mutant partner must do somewhat different experiments. You, your mutant partner and I will discuss your initial ideas in Thursday's lab, then you'll dig further into the literature and write up your ideas by next Tuesday.
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This page was last revised September 7, 2009. Its URL is http://udel.edu/~mcdonald/geneticslab1.html