Student Lesson Three
Collecting and crossing flies from the wild

In this lesson, flies collected from the wild will be crossed with cultured wild type and mutants. Data can now be compared with that from lesson two.

Materials:

1.  Stereomicroscope,
2.  Anesthetizing system
3.  Paint brushes
4. Culture vials with media
5. Various mutant strains of flies (as per lesson two)
6. Wild-type and caught
7.  Pictures of D. melanogaster and D. simulans
8. Fly Trap

Part 1: Collecting flies from the wild.

To obtain wild populations of flies you will need to construct a fly trap.  To do so, obtain a fly bottle, add a small bit of banana to the bottom, a few grains of yeast, and then tape a funnel to the top of the vial.

Take the trap home and place outside, out of direct sunlight and rain (or sprinkler systems).  Usually within a day you will find flies in your trap.  Plug the funnel hole and bring in to class. 

Part 2: A problem with wild flies, and a solution

Unfortunately, there is a separate species of Drosophila, D. simulans, which looks almost exactly like D. melanogaster to the untrained eye.  However, if these two mate, the hybrid offspring, if there are any, are sterile. (By the way, this fits well with the definition of species).  There are two ways to insure flies that have been caught are D. melanogaster and not D. simulans.

1.  Construct a cross of bought wild type D. melanogaster (using virgin females, of course) with males of the collected species.  Again, collect females, wait two days to insure virginity, and then mate.  Make at least two replicates. If larva are not present, the caught flies are D. simulans. However, if you obtain larva, then the collected flies are, indeed D. melanogaster.

2.  Using pictures provided by your instructor, identify males as either D. simulans or D. melanogaster

Your instructor will tell you the method to use. After you have caught flies, note the address (closest intersection) and date of capture in your journal.  In the classroom,

1.  Check to see if the flies have mites.  VERY IMPORTANT!!

2.  Transfer the flies to a fresh culture vial

3.  Anesthetize the flies and determine the species

In your journal, describe the difference between D. simulans and D. melanogaster and describe how you determined the difference in this lesson.

Part 3: Crossing collected flies with known phenotype flies.

In order to compare the genetics of your caught flies, make a cross using caught virgin females with bought wild-type males and bought mutants. Make reciprocal crosses and at least three replicates of each cross. Mate the F₁’s to obtain F₂ offspring and compare with crosses done with cultured wild type and mutant flies.

 

Part 4: Self assessment

At the end of this lesson your journal should contain:

1.  Location and date of capture of flies
2.  A written description in the difference between D. simulans and D. melanogaster
3.  The crossing you made
4.  The outcome and comparison between caught flies and bought wild-type flies

At the end of this lesson you should be able to:

1.  Construct fly trap
2.  Tell the difference between D. simulans and D. melanogaster
3.  Understand what a species is
4.  Make comparisons between different strains of wild type flies