1997 WWLPT Biology Institute:
Life Cycles: Reproduction & Embryological Development
Life Cycle of the Drosophila Fly
Summary/Abstract
Instructor's Objectives
Target Age or Ability Group Audience
Teacher Instructions/Special Precautions
Materials & Equipment Needs
Background [Prior Knowledge
or vocabulary necessary to complete activity]
The Student Lab
Method of Evaluation/Assessment
Extension/Reinforcement/Additional
Ideas
Summary/Abstract to
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Drosophila is an ideal model for embryology studies. It is found
all over the U.S. It is easy to take care of, and has a short life cycle.
These characteristics have made it a very popular organism in genetics
labs since Moorage and his fly parties.
In this activity the students will investigate the
life span and reproductive potential of fruit flies through their life
cycle.
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Instructor's Objectives
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This exercise is designed to help students observe
the life cycle of Drosophila. Students will learn how to manipulate
a large numbers of flies, tell the difference between the sexes, and identify
the different stages of the life cycle.
The intent of this activity is to give the students
a fun experience working with the flies as they investigate a few factors
that may affect their life span. At the end of this activity, students
should be encouraged to design their own experiments to test other environmental
variables that may affect the life cycle of the fruit fly.
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Target Audience or Age Group
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Life science courses, Introductory Biology, Honors Biology, Genetics,
AP Biology, Zoology
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Notes to the
Teacher: to top
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This investigation can run together in a series, or each of the five tests
given to a different team.
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Each team requires a mature stock culture of fruit flies.
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Demonstrate to the students how you want them to put the flies to sleep.
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You may want to give a prize to the student that had the longest-lived
fly.
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Materials & Equipment
Needs to top
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Jars to house the flies - commercial fly vials, juice bottles, or
any other small jar with an opening that a foam plug or cotton ball will
fit. If individual teams work on the entire exercise, they will need approx.
36 jars.
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Fly food - this could be bananas, apples, commercial prepared food,
potato flakes, etc.
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Dissecting microscope, or magnifying glass.
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Method of putting the flies to sleep - pert dish on ice, fly nap
(recommend using an anesthetize with this chemical), CO2 gas.
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Brush to manipulate the flies while observing them.
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3x5 cards to place the flies while sexing them.
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Tape to label the fly jars.
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Commercial foam plugs (recommended) or cotton balls to cap the jars.
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Background to
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Basic knowledge of the fruit fly anatomy for determining the sex of
the flies, and a review of their life cycle.
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The Student
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Part A: Determine the life span of fruit flies.
1. Collect five larva. Choose
the ones on the sides of the stock jar; they are the ones that are close
to pupating. Place them in a new jar. Do the same for your second jar.
As soon as a fly hatches, check its sex and then place it back in its vial.
Remove all of the other larva and place them in the morgue. Label the jar
as to date, sex, and test (#1). As the flies hatch in the second
jar, remove all flies that are the same sex as the one in the first jar
and place in the morgue. When you get a fly that is the opposite sex as
the one in the first jar, leave it in the jar and remove all remaining
larva. Label this jar as well. Each jar should now have only one
fly (one of each sex). Keep in mind that flies are no longer virgin after
8-10 hours; therefore, they should be checked often.
2. From your stock culture, take five virgin females
and five males. Place the five males in one vial and five females in another.
Do not forget to label date, sex, and test (#2).
3. One more time, from your stock culture, collect
five virgin females and five males. Place the five males in one vial and
the five females in another for a day. The second day, place the males
in the female vial for one day. The third day, separate the males into
their original vial. It will be necessary to remove all pupa that form
in the female's vial as they appear. Label this vial with the necessary
information.
4. In the fourth trial, repeat the third step, except
leave the five males with the virgin females. Observe the flies carefully
over the next few days. Record any behavior that you think is related to
mating. Compare your observations with other teams and reach a consensus
as to behavior related to mating. Record how many times those behaviors
are observed. Again remove any pupa that appear. For the seven vials in
steps 1-4, record the date the date of death of all flies. Take a class
average for each set.
5. From the stock culture, take an egg and
place it in a new vial and see how long it takes to hatch. You can tell
when this happens because the egg disappears or there is an empty egg case.
How long did it remain in the larval stage? Pupal stage?
6. Now that the vials are set up, tag the
flies so you may follow them through their life cycle. To help identify
each fly in steps 2-4, you may have to place a different color dot of paint,
one color for each fly, on the dorsal side of the thorax using a pin or
needle. Another way of tagging is to nick a different section of a wing.
Do the same for the females.
For all five steps, determine the life span of the flies and record.
Determine the class average for each sex in each group, and record.
Part B. Determine the pattern of egg production by the female.
1. From your stock culture, set up a virgin cross
of three males and two females. The next day, move the females to a new
vial and count the number of eggs presents in the old vial. Move the females
every day and count the eggs until the two females have died. At this time,
you should have approximately 28 vials. Make sure to mark each vial with
the date, and the number of eggs. to
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Methods of Evaluation/Assessment
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Test One:
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What is the average life span of the solitary virgin male and female fly.
Test Two:
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What is the average life span of the virgin male and female flies.
Test Three:
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What is the average life span of the male and female flies.
Test Four:
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What is the average life span of the male and female flies. Both males
and females were kept in the same vial.
Test Five:
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How long did it take the egg to hatch? How long did it take for the
larva to pupate? How long did it pupate?
Summary questions (Part A):
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Determine class averages for each set of data. Construct a data sheet containing
tables and graphs to show your analysis of the data.
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Record the mating behavior that you observed. Determine, as a class, what
behavior was related to mating.
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State your conclusion regarding the life cycle of Drosophila based
on: 1) sex, 2) having mated or not, 3) or being with both sexes during
their life time or not.
Summary questions (Part B):
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Does the ratio of males to females change over time? If so, give an explanation.
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Determine the class average of eggs laid per female, per day. Does the
number of eggs change during the fly's life span? Does the sex ratio of
the offspring change over the fly's life span? When is the egg production
the highest, lowest? For how does the fly produce its maximum number of
eggs?
Extension/Reinforcement/Additional
Ideas
Students are encouraged to design other experiments.
Possible variables are temperature, nutrients, photoperiod, etc.
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References Including Web Addresses
Biological Supply
Houses
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to top Vanessa
Bishop, Phil Talbot
Vanessa Bishop