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Itsy and Bitsy Ponder the Genetics of Fruit Fly Populations and Evolution

1994 Woodrow Wilson Collection


(Perform this dialogue. Follow all stage directions in the brackets.)

While awaiting the fruits of their labor, Itsy and Bitsy decide to take a trip to the high school's library. Bitsy recalled from a hunting expedition one day to the biology room that the teacher was talking about the toxic effects of citrus oils on insects and they have decided to learn more about culturing fruit flies.

Itsy: (With a questioning and curious look) Are we going to read about how those bottles we used in capturing fruit flies relate to bottlenecking and genetic drift?

Bitsy: (Showing a disgusted face, suggesting where are your brains?) No way, Lycosa rabida! (said sternly) We are just growing fruit flies in those bottles for our needs (as Bitsy smacks lips and rubs abdomen). If you want to learn more about evolution and genetic drift read The Neutral Theory of Molecular Evolution by Motoo Kimura.

Itsy: I do remember in (insert your teacher's name) ________________________________'s classes they used these critters in mating experiments. The students looked at the sex of flies, wing types, eye colors and body colors as traits. Even using my eight eyes I couldn't tell the differences among those bugs. Apparently using a dissecting scope helps in observing these distinguishing traits.

Bitsy: Hanging around the labs has had some rewards, but do you know the importance of traits and fruit flies in studying single-gene or the slightly more complicated two-gene cross?

Itsy: (With authority) Absolutely. Those flies are much more prolific than we wolf spiders. A fertilized female can lay hundreds of eggs on the medium in the culture vials. In two weeks hundreds of offspring of the next generation emerge and the traits can be observed and the data handled with more statistical confidence.

Bitsy:As with spiders these crosses require careful mating. (Rub the hairs on the back of your arms together and smile) For example a wild type male with normal wings is mated to a vestigial winged female. Oh, let's move to the chalkboard and I'll diagram this for you. (Get up and go to the chalkboard or get out a clean sheet of paper.)

(Here, give it your best shot. Use the following symbols W=normal wings and w=vestigial. The box below is the mating scheme. Carry out to the F2 results.)

Wild-type male Vestigial Female
Parents' Genotype
Punnett's square to obtain F1 This is an example
Not A Guideline!!!
F1's Genotype (F1 freely interbreed)
Punnett's square to obtain F2

(Itsy and Bitsy begin walking as if to the library.)

Itsy: (Nodding in agreement or not. If you disagree, explain or question Bitsy's diagram. When done, go on) Furthermore, I recall that experiment in (insert your teacher's name) ___________________________'s class. As the students did the crosses and counted the results, we grabbed a few tasty ones.

Itsy and Bitsy: (In unison and enjoyably) Mmm! Mmm! Mmmmmm!

Bitsy: (Motioning for Itsy to come along) We need to get back to our research. (Pointing to a chair) Have a seat here at the table. Begin searching the NY Time's Index. There was an article from the Tuesday Science Section posted on the bulletin board about citrus oils being toxic. If you don't find it within the past five years, try the CD-ROMS with the Magazine Index or Biological Abstracts. As automated as this process has become, you should be done soon.

Itsy: (Begins to protest the differential work load) But Bitsy! Wait! (Too late, Bitsy is muttering loudly while walking away)

Bitsy: I need to get back to the science wing of the school. Let me restate the problem. Growing fruit flies as food is the essence of our task. We want to grow as many flies as possible; yet if we use citrus fruits as our culture media we could be out of business before we get started. This is a classic illustration of natural selection for a defensive adaptation by the plants and the interspecific relationship of the predator to its prey. I'm hooked on this question! Those citrus plants are clever indeed to have developed a biological weapon against those pesky fruit flies, but obviously it is not thoroughly effective. So, Itsy, if you find answers in your reading before the biology classes conduct the next experiment, do wake me up. I want to know what we should do next.


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