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Axia College Material
Appendix I
FlyLab
Before beginning FlyLab:
1. Print out these lab experiment instructions. A printed copy of these instructions will aid in
completing the lab accurately and effectively, because you will not need to switch back
and forth between computer screens.
2. Disable your pop-up blocker. FlyLab and the FlyLab Online Notebook will open in new
browser windows. If you have a pop-up blocker, they will be blocked.
3. Read the online introduction and background information related to this lab
The experiment is divided into two sections: Self-Check Experiment and Exploration Experiment.
The Self-Check Experiment is designed to help you become familiar with the lab. The answers to
the Self-Check Experiment questions are given to you (in red text). Completing the Self-Check
Experiment and checking your answers will help you verify that you are completing the
experiments correctly.
The Exploration Experiment is the experiment you will be conducting and turning in to your
instructor for credit. You will report your findings for the Exploration Experiment in the FlyLab
report.
Getting to Know the Terminology
Can you roll your tongue? Some humans can stick their tongue in a rolled configuration: others
cannot. Evidence exists that this characteristic is determined by genetics, or your genotype. The
ability to roll your tongue, or not, is a trait inherited by offspring from their parents. Tongue rolling
is a dominant characteristic. If you inherit a gene for rolled tongue from either or both parents, you
might show this trait. The lack of ability to roll your tongue is recessive. Therefore, you would
need to inherit this gene from both parents before the trait could be expressed in your phenotype.
For this and other human traits, visit http://www.seop.yale.edu/supplementary/supp_traits.htm
Allele: The different forms that a gene might take. One allele for each trait is inherited from each
parent (Pruitt & Underwood, 2006).
Phenotype: The physical and physiological traits of an organism. For example, tongue-roller or
its opposite expression, non tongue-roller.
Genotype: The genetic makeup of an organism. The pair of alleles representing a trait could be
homozygous or heterozygous.
Homozygous: Both alleles in the pair are the same for a trait, both dominant or both recessive.
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Heterozygous: The genotype carries different versions of the trait in the allele pair. For example,
one dominant and one recessive allele.
Dominant allele: In a heterozygote, the allele that is fully expressed in the phenotype: For
example, tongue-roller trait is dominant and masks the non tongue-roller gene.
Recessive allele: In a heterozygote, it is the allele that is completely masked in the phenotype. In
order for the recessive trait to be expressed in the phenotype, both alleles must carry the
recessive trait. For example, non tongue-roller
Refer to the online glossary when you encounter other unfamiliar terms in this lab.
Getting to Know FlyLab
The following experiment is designed to help you become familiar with the operation of FlyLab.
To begin an experiment, you must first design the phenotypes for the flies that will be mated. In
addition to wild-type flies, 29 different mutations of the common fruit fly, Drosophila melanogaster,
are included in FlyLab. The 29 mutations are actual known mutations in Drosophila. These
mutations create phenotypic changes in bristle shape, body color, antennae shape, eye color,
eye shape, wing size, wing shape, wing vein structure, and wing angle.
For the purposes of the simulation, genetic inheritance in FlyLab follows Mendelian principles of
complete dominance. Examples of incomplete dominance are not demonstrated with this
simulation. A table of the mutant phenotypes available in FlyLab can be viewed by clicking on the
Genetic Abbreviations tab which appears at the top of the FlyLab homepage.
When you select a particular phenotype, you are not provided with any information about the
dominance or recessiveness of each mutation. FlyLab will select a fly that is homozygous for the
particular mutation that you choose, unless a mutation is lethal in the homozygous condition in
which case the fly chosen will be heterozygous. Two of your challenges will be to determine the
zygosity of each fly in your cross and to determine the effects of each allele by analyzing the
offspring from your crosses.
One advantage of FlyLab is that you will have the opportunity to study inheritance in large
numbers of offspring. FlyLab will also introduce random experimental deviation to the data as
would occur in an actual experiment. As a result, the statistical analysis that you will apply to your
data when performing chi-square analysis will provide you with a very accurate and realistic
analysis of your data to confirm or refute your hypotheses.
Self-Check Experiment: Performing Monohybrid and Dihybrid
Crosses
To begin a cross, you must first select the phenotypes of the flies that you want to mate. Follow
the directions below to create a monohybrid cross between a wild- type female fly and a male fly
with sepia eyes.
Note: The sepia eye mutation is a non-lethal recessive mutation located on chromosome III in
Drosophila
Design a Wild-type Female Fly
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1.
2.
3.
4.
Click on the Design button below the gray image of the female fly.
Click on the button for any trait on the left side of the Design view.
The small button next to the words "Wild Type" should already be selected (bolded).
To choose this phenotype, click the Select button below the image of the fly at the bottom of
the Design view screen.
5. Remember that this fly represents a true-breeding parent that is homozygous for wild type
alleles.
6. The selected female fly now appears on the screen with a "+" symbol indicating the wild-type
phenotype.
Design a Male Fly with Sepia Eyes
1. Click on the Design button below the gray image of the male fly.
2. Click on the Eye Color button on the left side of the Design view.
3. Click on the small button next to the word "Sepia."

Note how eye color in this fly compares with the wild-type eye color.
4. Choose this fly by clicking on the Select button below the image of the fly at the bottom of the
Design view screen.
5. The male fly now appears on the screen with the abbreviation "SE" indicating the sepia eye
mutation.


This fly is homozygous for the sepia eye allele.
These two flies represent the parental generation (P generation) for your cross.
6. Based on what you know about the principles of Mendelian genetics, address the following
points:


Predict the phenotypic ratio of wild eye to sepia eye flies that you would expect to see for
the F1 offspring of this cross.
Describe the phenotype of each fly.
You should predict that all F1 offspring from this cross between homozygous parents should show
the wild-type phenotype. Keep in mind that, although the genotype of the offspring will be
heterozygous for sepia eye, the wild eye trait is dominant.
Select the Number of Offspring
1. Click on the drop-down menu on the left side of the screen and select 10,000 flies.
2. To mate the two flies, click on the Mate button between the two flies.



Examine the fly images that appear in the box at the bottom of the screen.
Scroll up to see the parent flies.
Scroll down to see the wild-type offspring. These offspring are the F1 generation.
3. Answer the following question:

Are the phenotypes of the F1 offspring what you predicted for this cross?
The wild-type eye trait is a dominant gene; therefore, all F1 offspring will have the wild-type
phenotype.
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4. It might be helpful if you look at the cross in a Punnett Square. The wild-type female parent is
represented with + and the sepia eye color male parent with se.
Female
Male
se
+ se
se
+ se
+ se
+ se
+
+
Notice that each offspring receives one allele from the male parent and one allele from the female
parent. The dominant allele will mask the characteristic of the recessive allele for the trait, and the
fly phenotype will show the dominant or wild-type characteristic.
5. Practice saving the results to your lab notebook by following these steps:




Click on the Analyze Results button on the lower left side of the screen. A panel will
appear with a summary of the results for this cross. Note the number of offspring,
proportion of each phenotype and observed ratios for each observed phenotype.
Click the Add Data to Notebook button.
Type in any comments you would like about the results, such as, "These are the results
of the F1 generation for my first monohybrid cross."
Important: After you have saved your results, do not close your lab notebook. To
continue with your experiment, minimize your notebook.
Cross Offspring
Complete the following steps to set up a cross between two F1 offspring to produce an F2
generation.
1. Be sure that you are looking at the two wild-type offspring flies in the box at the bottom of the
screen. If not, scroll to the bottom of the box until the word "Offspring" appears in the center
of the box.
2. Click the Select button below the female wild-type fly image.
3. Click the Select button below the male wild-type fly image.

Note that the two F1 offspring that you just selected appear at the top of the screen as the
flies chosen for your new mating.
4. Click on the Mate button between the two flies.

The F2 generation of flies now appears in the box at the bottom of the screen.
5. Use the scroll buttons to view the phenotypes of the F 2 offspring.
6. Click on the Analyze Results button on the lower left side of the Mate view to examine the
phenotypes of the offspring produced.
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7. Click on the Ignore Sex button.
Notice that the
number of flies
that show the wild
eye trait is about
three times larger
than flies with the
sepia trait.
Based on Mendelian genetics, you should expect to see a 3:1 phenotypic ratio in the F2 offspring,
where 75% of the offspring show the wild-type phenotype and 25% of the offspring show the
sepia eye mutation (homozygous recessive genotype)
8. Click the Add Data to Notebook button.
9. Type in any comments you would like about the results, such as, "These are the results of the
F1 generation for my first monohybrid cross."
10. Important: After you have saved your results, do not close your lab notebook. To continue
with your experiment, minimize your notebook.
Chi-Square Analysis
To validate or reject a hypothesis, perform a chi-square analysis as follows:
1.
2.
3.
4.
Click on the Chi-Square Analysis tab on the upper right side of the screen.
To ignore the effects of sex on this cross, click on the Ignore Sex button.
Enter a predicted ratio for a hypothesis that you want to test.
For example, if you want to test a 3:1 ratio (dominant wild-type to recessive sepia eye), enter
a three (3) in the first box under the Hypothesis column and enter a one (1) in the second
box.
5. Answer the following questions:

What values are produced by this test?
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The phenotype, the observed ratio, the hypothesis ratio, the expected ratio, chi-squared test
statistic, degrees of freedom, level of significance, and recommendation on the hypothesis.

What was the recommendation from the chi-square test?
Accept the 3:1 hypothesis.
Optional: To evaluate the effects of sex on this cross, select the Use Sex button on the Summary
of Results tab. Does the hypothesis hold true for males and females? Yes.
6. Before closing this screen test a different hypothesis using the chi-square analysis by
following these steps:




Click on the Test a New Hypothesis button on the lower right side of the Chi-Square
Analysis screen.
To ignore the effects of sex on this cross, click on the Ignore Sex button.
Enter a predicted ratio for a hypothesis that you want to test, for example, 4:1.
Click the Test Hypothesis button at the bottom of the panel. A new panel will appear
with the results of the chi-square analysis.
7. Answer the following questions:

What changes in the values do you see?
The chi-square statistic increased and the level of significance decreased.

What was the recommendation from the chi-square test?
Reject the hypothesis of a 4:1 ratio
8. Click the Add Data to Notebook button.
9. Place the cursor below the recommendation line and type the following: "These are my
results for the F2 generation of my first monohybrid cross. The data seem to follow a ratio of 4
to 1."
10. To save or copy and paste your lab notes, you can export this data table as an html file by
clicking on the Export Notes button. In a few seconds, a new browser window should appear
with a copy of your lab notes. You can now save a copy of your lab notes or copy and paste
your notes into another document.
11. Based upon the results, answer the following questions:


What did you discover to be the correct phenotypic ratio for this experiment? 3:1
What do the results of this experiment tell you about the dominance or recessive effects
of the sepia allele for eye color?
You should determine that the sepia allele is a recessive allele. Similar experiments can be
designed using other recessive mutations.
Further Practice
1. Click on the Return to Lab button.
2. Click on the New Mate button in the lower left corner of the screen to clear your previous
cross.
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3. Following the procedure described above, perform monohybrid crosses for at least three
other characteristics.
4. For each cross, develop a hypothesis to predict the results of the phenotypes in the F1 and F2
generations.
5. Perform chi-square analysis to compare your observed ratios with your predicted ratios.
6. For each individual cross, try varying the number of offspring produced.
7. Answer the following questions:


What effect, if any, does this have on the results produced and your ability to perform chisquare analysis on these data?
If any of your crosses do not follow an expected pattern of inheritance, provide possible
reasons to account for your results.
With a monohybrid cross for a non-lethal, non sex-linked dominant allele, all of the F1 offspring
will show the phenotype for the dominant mutation. The F2 generation will show a 3:1 phenotypic
ratio where 75% of the offspring will show the phenotype of the dominant mutation and 25% of
the offspring show the recessive phenotype.
Note: Observed ratios may vary depending on whether you choose:



Recessive or dominant mutations for monohybrid crosses.
A mutation that is lethal, in which case some offspring die and the numbers are reduced.
A mutation that is sex-linked, in which case the male and female offspring are affected
differently.
Dihybrid Cross
Once you are comfortable with using FlyLab to perform a monohybrid cross, design a dihybrid
cross by completing the following steps. Refer to pp. 73-75 in Bioinquiry for more information on
dihybrid crosses.
1. Click the New Mate button.
2. Follow the same steps as you did in the monohybrid cross to mate an ebony body and
normal wings female fly with a male fly that has the normal body color and vestigial mutation
for wing size.
3. Develop a hypothesis to predict the results of this cross and describe each phenotype that
you would expect to see in both the F1 and F2 generations of this cross.
4. Analyze the results of each cross by chi-square analysis and save your data to your lab notes
as previously described in the assignments for a monohybrid cross.
5. Answer the following questions:


Describe the phenotypes that you observed in both the F 1 and F2 generations of this
cross.
How does the observed phenotypic ratio for the F2 generation compare with your
predicted phenotypic ratio? Explain your answer.
The ebony body and vestigial wing mutations are non-lethal recessive mutations. All offspring in
the F1 generation will show wild-type phenotypes for body color and wing size. A cross between
F1 heterozygotes will yield an F2 generation with a 9:3:3:1 phenotypic ratio.
Exploration Experiment: Testcross
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A testcross is a valuable way to use a genetic cross to determine the genotype of an organism
that shows a dominant phenotype but unknown genotype. For instance, using Mendel’s peas, a
pea plant with purple flowers as the dominant phenotype could have either a homozygous or a
heterozygous genotype. With a testcross, the organism with an unknown genotype for a particular
phenotype is crossed with an organism that is homozygous recessive for the same trait.
In the animal- and plant-breeding industries, testcrosses are one way in which the unknown
genotype of an organism with a dominant trait can be determined. Perform the following
experiment to help you understand how a testcross can be used to determine the genotype of an
organism.
1. Click the New Mate button.
2. Follow the steps detailed in the first experiment to design a female fly with brown eye (BW)
color (keep all other traits as wild-type), and design a male fly with ebony body (E) color
(keep all other traits as wild-type).
3. Click on the drop-down menu on the left side of the screen and select 10,000 flies.
4. Mate the two flies.
5. Examine the F1 offspring from this cross and follow the steps detailed in the first experiment
to save your data to your lab notebook.
6. Add any comments that you would like to your data and copy and paste your data into the
Data section of the Appendix J: FlyLab Report.
7. Answer the following question in Appendix J: FlyLab Report:

Describe the phenotypes that you observed in the F1 cross.
To determine the genotype of the F1 wild-type female fly, following these steps:
8. Select the F1 wild-type female fly, by clicking the Select button below the fly.

Note that the F1 offspring that you just selected appears at the top of the screen as the fly
chosen for your new mating.
9.
10.
11.
12.
13.
Click the Design button under the gray image of the male fly.
Design the male fly with brown eye color and ebony body color.
Cross this fly with the F1 wild-type female fly by clicking the Mate button.
Click the Analyze Results button.
Follow the steps detailed in the first experiment to examine the results and save the results to
your lab notebook.
14. Add any comments that you would like to your data and copy and paste your data into the
Data section of the Appendix J: FlyLab Report.
15. Answer the following questions in Appendix J: FlyLab Report:




Describe the phenotypes that you observed in the testcross.
What was the phenotypic ratio for the offspring resulting from this testcross?
Based on this phenotypic ratio, was the F1 wild-type female homozygous or heterozygous
for the eye color allele? Explain your answer.
Based on this phenotypic ratio, was the F1 wild-type female homozygous or heterozygous
for the body color allele? Explain your answer.
References
Pruitt, N. L., & Underwood, L. S. (2006). Bioinquiry: Making connections in biology (3rd ed.).
Hoboken, NJ: John Wiley & Sons, Inc.
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FlyLab assignments and answers were adapted with permission from Pearson Education, Inc.
Biology Labs On-Line is a collaboration between the California State University system and
Benjamin Cummings.
© 2002 California State University and Benjamin Cummings, an imprint of Pearson Education,
Inc. Development was partially supported by a grant from the U.S. National Science Foundation.
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