Fruit Fly Genetics 2Green Group

twogreen3, twogreen1, twogreen2, and twogreen4


We studied the mutation of vestigial wings which is where the fly's wings are crumpled and useless. We used these flies because they reproduce very fast, so we could study several generations of flies in a reasonable amount of time (a little over two weeks per generation).

Characteristics of Drosophila

Our flies are phylum/arthropoda which means that they are arthropods and that they have segmented bodies (jointed appendages) and exoskeletons. They are of the class insecta (insects) and order diptera, which means they have one set of wings, carry diseases and pollinate flowers.  

Fly Phenotypes

We've been studying 3 different phenotypes for the Drosophila melanogaster (fruit flies). Phenotypes are basically different mutations or variations. For example, phenotypes for people would be things like, people with brown hair instead of blonde hair, or blue eyes as opposed to brown. You get the point. Same basic ideas, only for the flies we were studying white eyes, wild being average or insect before mutation, and vestigial wing, vestigial meaning useless and deformed wings. My group specifically studied the vestigial winged flies and the wild flies. We discovered that vestigial wings are an autosomal recessive trait which means the immediate offspring of a wild fly and vestigial fly will not have vestigial wings but the second generation might, but discovered that this probably isn't the right word since we knew this before we did the experiment and our vials were contaminated with extra vestigial flies that we weren't planning on. Because of this our results came out a little off.

Life Cycle Log

    Date: 3/16/06         Vial #1: female=vestigial, male=wild      Vial #2: female= +, male=vg

   Vial #1: 6 flies are in vial, missing female vg, we need to add them to vial. No flies are dead so far. Wings are wild (normal) eyes are red, seem to be healthy.

   Vial#2: missing male vg, 6 female flies, non are dead. Seem to be healthy.

   Date: 3/17/06

   Vial#1: have added vg female (this morning) but we still need 2 more, still asleep from fly nap.

   Vial#2: have added one vg male, but still need 5 more.

   Date: 3/23/06

   Vial#1: Have taken out P generation of flies to prepare for generation F1. Larvae are in the white mush,, there seem to be a lot of larvae. There is one dead parent fly at the bottom in the mush.

    Vial#2: Have done the same thing to this vial, as we did to vial 2. Medium (mush) is very dry, we have added water. 4 dead flies.

   Date: 3/24/06

   Vial#1: plenty of larvae making their way up the vial, 1 pupa. Some others are turning into pupa.

   Vial#2: Medium is more moist, can only spot a few larvae, maybe 3, very small.

   Date: 3/27/06

   Vial#1: Huge ring of pupae where the larvae once were, looks like they might hatch soon. The medium is still very mushy with plenty of active larvae.

   Vial#2: Still larvae in medium, the medium is not so mushy, it looks like the larvae have been digging through it a lot. Small ring of pupae just above medium, some look like they might hatch soon.

   Date: 3/28/06

   Both look the same as yesterday, vial#1 looks like the pupae will hatch soon.

   Date: 3/30/06

    Vial#1: The majority of flies have come out of their pupa stage, still a lot of pupae on the sides and a few larvae in the medium. Most of the flies are wild type, 1 or 2  vestigial.

    Vial#2: About  30 flies, pupae on the sides.

   Date: 3/31/06

   Vial#1: Ring of pupae, a lot of flies at the top of the vial, some are vg.

   Vial#2: Not as many flies as vial#1, bottom looks kinda crunchy, can't see any vg right now.


Sexing is when you are able to tell what sex the fly is and separating the flies into their own sex categories. It isn't that hard to tell a male fly from a female fly, you can tell what sex they are by their abdomen. A male's abdomen is usually more narrow than that of the female's and the tip of the male's abdomen is darker. The female's abdomen is wider than the male's and their tip of the abdomen is much less darker than the males. 

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This is image # 12021 if you want to move it. © 2006 twogreen1

F1 Predictions

In the parent crosses we had one vial labeled "Vial 1" which consisted of vestigial females and wild males, then we had another vial that we labeled "Vial 2" which had wild females and vestigial males. The predictions for these flies were, if the gene for vestigial wing was for an autosomal (non-sex chromosome), our first hypothesis was, if the mutation for vestigial is dominant and the wild is recessive, then the phenotype for the flies would be 100% vestigial and the genotype would be 100% vg+.

   Vg Vg 
 +  Vg+  Vg+
 +  Vg+ Vg+

Our second hypothesis for the other vial was if the wild is dominant and vestigial is recessive, then the phenotype would be 100% wild heterozygous and the genotype would be 100% +vg.

   +  +
 Vg  +Vg  +Vg
 Vg  +Vg  +Vg

    Our next predictions were if vestigial wings were sex-linked on the X chromosome. Our hypothesis was if the mutation for vestigial is sex-linked and dominant and wild is recessive, and the mutation is on the female,

  Xvg  Xvg 
X+  XvgY  XvgX+ 
 Y  XvgY  XvgY

then the phenotype percentage would be 50% vestigial female, and 50% vestigial male, and the genotype percentage would be 50% female is heterozygous XvgX+, and 50% male is XvgY. We then looked at a mutation on a male in the same situation as the mutated female which looked like this,

 X+Xvg  X+Y
 X+ X+Xvg   X+Y

We now know for the male's percentage for it's phenotype would be 50% vestigial female and 50% wild male, and the genotype percentage would be 50% female is heterozygous X+Xvg, and 50% male is normal X+Y.

Our next sex-linked hypothesis would be if the wild (+) is sex-linked and dominant, and the mutation for vestigial (vg) is recessive, then if the mutation was on the female it would look like,

 Xvg  X+X+ XvgY 
 Xvg  X+X+  XvgY

After looking at the punnett square, we know that the percentage for the phenotype would be 50% wild female and 50% vestigial male, and the female is heterozygous X+Xvg and 50% male is heter. XvgY. Then we looked at what might happen when the mutation was on the male, then the punnett square for this would look like this,

  X+  X+ 
 Xvg  X+Xvg X+X 
 X+Y X+Y 

 The percentage for the phenotype would be 50% wild female and 50% wild male, and the genotype percentage would be 50% female is heterozygous X+Xvg and 50% male is normal wild homozygous X+Y.

F1 Outcomes

Our F1 generation or direct  offspring as mentioned before didn't come come out the way we expected because our original vial1 got contaminated with vestigial flies and so we got vestigial flies in our F1 generation.

F2 Predictions

The F2 predictions are the next generation in the fruit flies. Since we know what the genotypes for the F1 generation are, we can now make predictions for the F2 generation. The vials contain the same flies, but we want to know what the offspring of the F1 generation will be.

If vial 1 had the F1 cross of female wild wing (genotype heterozygous) and a male wild wing (genotype heterozygous) then the punnett square for this cross would be...

 Vg  vgvg  +vg
 +  +vg  ++

 This shows that the percentages for the flies phenotypes would be 25% vestigial wing, 75% wild wing. The punnett square also shows the percentage of the flies genotype, which is 25% homozygous vestigial recessive, 50% heterozygous wild dominant, and 25% homozygous wild dominant.

We then have to see what vial 2 might contain. We know that the cross for this vial is different from vial 1, so the cross for the female would be wild (genotype +vg), and the male would be wild (genotype +vg). With this information, we can make the punnett square and predict what the offspring will be.

   +  vg
 +  ++  vg+
 vg  vg+  vgvg

Looking at the phenotype crosses, the predictions for the F2 generation phenotypes for vial 2 would be 25% vg, 75% +. Then the genotypes would be 25% homozygous vg recessive, 50% heterozygous wild dominant, and homozygous wild dominant.

F2 Final Count

Vial 1 for the F2 generation produced 95 wild females and 129 wild males, it also produced 30 vestigial females and 31 vestigial males. Vial 2 produced 94 wild females 117 wild males and 47 vestigial females and 43 vestigial males.

Percent Error 

Vial 1

 Phenotype Observed  Expected  (O-E)  (O-E)/E  X100
 Vestigial  61  71  10  .1408  14.08  14%
 Wild  223  213  10  .0469  4.69  5%

Vial 2

 Phenotype  Observed Expected   (O-E) (O-E)/E  X100   %Error
 Vestigial  90  75.25  14.75  .19601  19.60  20%
 Wild  211  225.75  14.75  .06533  6.53  7%


Our restated hypothesis is, if the mutation vestigial is autosomal recessive in the P generation, then by the F2 generation the expected Phenotype Ratio 75% wild and 25% vestigial. Based on the information and the percentages that we got, we think that although there was a contamination and that there shouldn't be as many vestigial in the F1 and F2 generations, we can say that our hypothesis is supported well enough. The problems that we faced were that there was a contamination and and flies flew out, and not counting accurately. Our groups thinks that if we could've done anything differently, we would make sure that we had the right amount of female and male flies with their right phenotypes before we put them into the medium. While experimenting with the flies, one of the questions that we wondered was whether the flies were becoming immune to the fly nap, because it got to a point where the flies wouldn't go to sleep after 10 minutes.


Here lies a lot of dead flies. They did it for science!

About This Page

Author: twogreen3, twogreen1, twogreen2, and twogreen4
Classroom Project: twogreen
city high school
Tucson, AZ USA

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