Mutagenic Effect of UV Exposure on Metabolic Activity of Fruit Flies (Drosophila
melanogaster)
Xin Gong
Department of Biological Sciences
Saddleback College
Mission Viejo, CA 92692
Ultraviolet light has been known to impact a living organism either negatively, as
seen in plant growth, or positively, as seen in many forms of cancer. In fruit flies, UV
radiation has also been observed to have a negative effect on reproduction. This experiment
investigated the mutagenic effect of ultraviolet light on metabolic activity, using fruit flies
as the model organism. Metabolic activity was determined by how quickly the fruit flies
regained consciousness after administration of FlyNap®. Arousal times were measured
after the flies had been exposed to UV light for a certain amount of time. Results showed
that longer exposure rates actually decreased arousal time, suggesting that UV radiation
has an activating (excitatory?) effect on fruit fly metabolism. These differences are
reflected by varying exposure times. Further genetic testing would need to be done to
confirm whether these differences are in fact a result of mutagenesis, or if it is the result of
a chemical change.
Introduction
Since metabolism is facilitated in large part by enzymes, which are coded for by DNA, inducing a mutation
in these genes can either activate or inhibit translation of the metabolic enzymes. In a hospital setting, variations in
metabolism of IV anesthetics, such as Propofol®, administered in metered dosesm (doses) are commonly observed
in patients during surgery, which is why the metabolic rates of each patient must be tested before going into surgery
(Run on sentence, might want to split it into two separate thoughts). Similar effects can be observed in fruit flies
when they are administered a metered dose of FlyNap®. Individuals with similar genetic makeup are expected to
metabolize the anesthetic at a similar rate. However, mutations in genes that control metabolism can either increase
or decrease the rate of metabolism, depending on whether the mutation is activating (excitatory?) or inhibitory.
Drosophila melanogaster serves as a useful model organism in biology due to its short generation time as
well as its relatively simple karyogamy, which consists of only three pairs of autosomes and one pair of sex
chromosomes, allowing for easy genetic manipulation and testing. There have been many compelling studies on the
mutagenesis of fruit flies in molecular genetics; however, not many studies have been *focused on* the mutagenesis
of fruit flies in *regards to* metabolism (Grigliatti, “Temperature-sensitive mutations in Drosophila melanogaster”
Just include author and the year in citations). These studies may bring to light many findings in the metabolism of
other organisms as well.
Since the major effect of UV radiation is to create thymine dimers, which inhibit DNA replication and
transcription, it was hypothesized that UV radiation would have an inhibitory effect on metabolic activity *of fruit
flies*. Longer exposure times (Times of exposure) to UV would lead to longer arousal times following anesthesia.
(in the hypothesis, you may want to specify that the focus of the project is on the flies)
Materials and Methods
The following 40-mL vials with cotton stoppers containing 15-20 flies with 10 mL of nutrient media
containing starch and active yeast were prepared: a control, 5-, 10-, and 20- second exposure groups (May want to
consider rewriting this first sentence to clear it up a little bit. It is a bit wordy and could be split up nicely into a
couple sentences). After being properly labeled, each group of flies was fully sedated with FlyNap®, an anesthetic
mixture consisting of 50% triethylamine, 25% ethanol, and 25% fragrances (FlyNap® MSDS). FlyNap®
administered through a Fly Wand suspended in the vial just below the plug for approximately 45-90 seconds. To
ensure that the last fly (all flies?) had been anesthetized, the vial was gently tapped to check for any movement.
The control group was not exposed to any radiation while the three variable groups were exposed to UV
light at 254 nm for 5, 10, and 20 seconds (Maybe include how you exposed hem to the UV, for example, were all
flies removed from their containers and exposed). Following exposure, the flies were incubated for 3 days to recover
and fully express any mutations. Flies were again knocked out (sedated) with FlyNap® using the same procedure
above (t0), and then monitored vigilantly for the next few hours. Using a stopwatch, the time of arousal for each fly
was recorded when the first sign movement was observed (t1,2,3,…). The time it took for each individual fly to regain
consciousness, in minutes, was calculated by subtracting t0 from tx.
Results among the control and three experimental groups were and analyzed by a single factor analysis of
variance (ANOVA) test followed by a paired post-hoc test.
Results
Arousal Time (in mins)
In contrast to the initial hypothesis, arousal time decreased with increased exposure to UV (Figure 1).
While there was no significant difference between the average arousal times between the 5- and 10- second groups,
the flies in the control group took significantly longer to regain consciousness while those in the 20 second group
took a significantly shorter amount of time. Results of the ANOVA test were significant with a P value (p-value) of
0.0015 (May want to add asterisk above error bars in graph where data shows a significant difference).
A paired post-hoc test determined that at a 95% confidence interval, there was no significant difference
between the control and 5-second groups; however, the differences between the control and 10-second groups and
the control and 20-second groups were significant (Table 1).
200
150
100
50
0
Control
5 sec
10 sec
20 sec
Exposure Groups
Figure 1: Bar graph displaying mean ± SEM arousal time for control and experimental groups.
Table 1: Results of the post-hoc test (Bonferri Correction) comparing the control group with the three experimental
groups *Results were significant between the control and 10 second group and between the control and 20 second
group at α=0.05 and insignificant between the control and 20 second groups*
Comparison
Significant?
(P <0.05?)
t
1: C & 5 sec
No
2.401
2: C & 10 sec
Yes
2.573
3: C & 20 sec
Yes
4.079
Discussion
In the time that it took for the fruit flies to regain consciousness following anesthesia from FlyNap®, there
were significant differences in arousal times between the control group and the 10- and 20- second group. However,
while the initial hypothesis was that longer exposure to UV light would lead to longer arousal times, the arousal time
actually shortened with longer exposure time. This suggests that UV mutagenesis has an activating (excitatory?)
effect on ability of the fruit fly to metabolize FlyNap®.
If mutagenesis occurred, the mutation may have affected a gene coding for suppression of metabolism,
leading to an increase in metabolic activity (Stryer, Biochemistry). However, it is not entirely clear whether the
significant increase in metabolic activity is, in fact, due to a mutation or if it is a result of a chemical alteration of the
metabolic enzymes within the fruit fly. Further genetic testing must be performed to determine whether this change
is genetic or chemical.
Literature Cited
Berg, J.; Tymoczko, J.; Stryer, L. Biochemistry. W. H. Freeman and Company 2012.
Grigliatti, T.; Hall L., Rosenbluth, R.; Suzuki, D. “Temperature-sensitive mutations in Drosophila melanogaster.”
No quotation marks around titles of papers) Molecular and General Genetics. 1973. 120 (2): 107-114.
Ziilstra, J.A.; Vogel, E.W. “Influence of inhibition of the metabolic activation on the mutagenicity of some
nitrosamines, triazenes, hydrazines and seniciphylline in Drosophila melanogaster.” (quotation marks) Department
of Radiation Genetics and Chemical Mutagenesis, University of Leiden, The Netherlands. 1988 Nov; 202(1):251-67.
FlyNap® Material Safety Data Sheet
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Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s):___Xin Gong__________________________________
Title:_Mutagenic Effect of UV Exposure on Metabolic Activity of Fruit Flies (Drosophila melanogaster)
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
Fruit flies were sedated with FlyNap. The flies were grouped in groups of 15-20 in four separate
containers. Three containers were subject to UV radiation from a light source for, 5-,10-, and 20- second
durations. After UV exposure, the flies were allowed three days to incubate to recover fully. After the 3
days, flies were again sedated and were watched to see how long it would take for them to digest the
FlyNap and regain consciousness. This is a direct correlation to the flies rate of metabolism. These
results were analyzed using ANOVA and a Bonferrroni correction. It was found that despite the
hypothesis that UV would lengthen time of metabolism, the data supported the opposite. Evidence
suggests that UV exposure actually decreased the length of time of metabolism.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current
state of knowledge.
Paper was very well composed and straight forward. Everything was presented clearly and concisely.
There were a few grammatical errors, but noting too serious. The only thing I would suggest is breaking
up some of the run on sentences into two separate sentences rather than trying to cram in so much
information into 1 sentence.
Also, I would look to do some further research in regards to the discussion. I would try to make links
between the results you had found and other studies to see if anyone else had found the same
surprising results. You only have three real sources cited, I’m not sure what the minimum is but you
may want to see if you can find some more background studies to reference in the intro as well.
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical errors, and
minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.
This paper was a final version
This paper was a rough draft
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I centered everything, you might need to change the format when you submit the final draft
Recommendation
 This paper should be published as is
 This paper should be published with revision
 This paper should not be published
Signature:______________________________________ Date:__12/8/2013________________