Fruit Fly Behavior Lab
Design and run a Drosophila behavior experiment using a virtual choice chamber. Test whether fruit flies prefer light, humidity, food odors, or vinegar. Track fly positions over time, collect data at regular intervals, and apply the chi-square goodness-of-fit test to determine whether the observed distribution differs significantly from random.
Guided Experiment: Investigating Drosophila Phototaxis
If fruit flies are placed in a choice chamber with one lit side and one dark side, do you predict they will prefer the light, the dark, or show no preference? Why?
Write your hypothesis in the Lab Report panel, then click Next.
Controls
Results
Data Table
(0 rows)| # | Time(min) | Chamber A (Stimulus) | Chamber B (Control) | Total | % in Stimulus |
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Reference Guide
Drosophila Behavior
Drosophila melanogaster (the common fruit fly) is a model organism used extensively in genetics and behavioral biology. Adult flies exhibit several well-documented behavioral responses.
- Positive phototaxis - flies move toward light sources
- Negative geotaxis - flies climb upward against gravity
- Chemotaxis - flies are attracted to fermenting fruit odors (ethanol, acetic acid)
These innate behaviors are controlled by sensory neurons and can be quantified using choice chamber experiments.
Chi-Square Goodness of Fit
The null hypothesis (H₀) states that flies distribute equally between chambers (50:50). The chi-square test measures how far the observed counts deviate from this expectation.
For a two-chamber experiment with n total flies:
Reject H₀ if the computed chi-square exceeds 3.841 (the critical value for df=1 at the 0.05 significance level).
Taxis and Kinesis
Taxis is a directional movement toward or away from a stimulus. Positive taxis = toward, negative taxis = away.
Kinesis is a change in movement rate or turning frequency, without a directional component. Organisms showing kinesis slow down in favorable conditions, causing accumulation.
Drosophila phototaxis is a true taxis response because flies actively orient and move toward the light, not just slow down near it. This can be confirmed by observing individual fly trajectories in the choice chamber.
Experimental Design
A good behavior experiment should include:
- Control - one chamber with no stimulus for comparison
- Replication - enough organisms (20+) and repeated trials
- Time series - record counts at regular intervals, not just the endpoint
- Controlled variables - temperature, humidity (except when tested), and container size stay constant
The time series data helps distinguish between organisms that settle quickly versus those that continue moving throughout the experiment. Reporting the final counts alone can miss important temporal patterns.