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STUDENT OBJECTIVE

Using a chi-square analysis, students interpret the responses of Drosophila to light and gravity. If time permits, students can investigate chemotaxis using a simple tee-choice apparatus.

EQUIPMENT	AMOUNT
	(Class of 24 with 8 groups)
Lamp, swing arm with 100 watt bulb	8/lab
MATERIALS
Fruit flies, live Vials, plastic 10 cm x 3 cm diameter and stopper (CBS#17-3085, 3086) Tee tubes, 8 mm, rubber stoppers to fit plastic vials above Tape (clear) Marking pencil Ruler Cardboard tube, 30 cm x 4 cm diameter (from center of paper towel roll) Stoppers, rubber #8 or #9 Ring stand Clamps Ring, 3" diameter iron Thermometer Beaker, 400 ml Beaker, 800 ml Stick, wooden, 1/8" diameter x 6" Crisper, plastic (to hold materials) Black cloth 24" x 24"	15 flies/group 2/group 1/group 1 roll/lab 1/group 1/group 1/group 2/group 1/group 2/group 1/group 1/group 1/group 1/group 1/group 1/group 1/group

For instructor use only

*Please refer to the Appendix for name and address of supplier.

PREPARATION

Two Weeks before Lab

Instructions are given in Lab Topic #9 for culturing Drosophila successfully. Use wild-type flies. There is no need to separate sexes for this exercise. A stock culture chamber should be started with 20 females and 10 males. Place in a 22—24^oC area with adequate moisture. After 7—8 days, remove all the adults. Emergence of new adults should occur in 12—13 days.

One Week before Lab

1. The ends of the cardboard tubes should be reinforced with a wrapping of fiber strapping tape. Two holes should be punched across from each other, one-eighth inch in from the edge of one end of the tube. The completed chamber should have a rubber stopper on each end that fits securely and permits no light passage.
2. Assemble tee-tube apparatus as shown in lab manual (fig. 30.4).

Several Hours before Lab

The Drosophila should be lightly anesthetized and 15 counted into each vial. Before giving to the students, observe to make certain flies are alive.

NOTES

1. The cardboard tube used as a sleeve for the plastic vials can be cut from a mailing tube, or an empty paper toweling tube can be used.
2. All vials should be washed and rinsed well to remove the possibility of the flies responding to contaminants in the vial.
3. A piece of tissue over the open end of the cardboard tube during the experiments is an excellent light diffuser.

CLASSROOM SUGGESTIONS

1. Drosophila can be difficult to count because they respond to the slightest disturbance. Students can divide the responsibility of counting each section of the tube during the trials. Instructors might want to increase the number of flies observed to obtain a larger set of data. Each group can test two vials and not increase the laboratory time by very much.
2. Check out the links for this lab topic at http://auth.mhhe.com/biosci/genbio/dolphin/ You will find useful materials for developing your lab introduction or summary, and in some cases, you may want to tell students to connect to a particular site for further information.

ANSWERS TO CRITICAL THINKING QUESTIONS

1. Attempt to control for heat in several ways. Water container between flies and light source filters out much of the heat. Using a thermometer to check temperatures will tell whether heat is an influence. There is a still possibility that infrared energy is passing into the vials and triggering the flies’ movement.
2. The tee-tube chambers contained were saturated by placing wet cotton in them. There should be no difference between the chambers due to humidity.
3. These two taxes favor emergence. Fruit flies inside a rotten fruit or under a layer of rotting vegetation will move in such a way as to escape entrapment.

SUPPLEMENTAL MATERIALS