Drosophila Simulation: Patterns of Heredity
Objective: Students will learn and apply the principles of Mendelian inheritance by experimentation with
the fruit fly Drosophila melanogaster. Students will make hypotheses for monohybrid, dihybrid and sexlinked traits and test their hypotheses by selecting fruit flies with different visible mutations, mating
them, and analyzing the phenotypic ratios of the offspring. Students will record their observations into
an online notebook and write a lab report.
Website: http://www.sciencecourseware.org/vcise/ --- Click on the Drosophila Link
Registration
1. Create a new account
2. Class code # _____________________________
3. Enter your first and last name (your username will be generated for you)
4. Choose a password ' Write down your user name and passwords!
Notebook: The top tab contains a "notebook" link where you can enter data gathered during your
experiments. Also in the notebook tab, you will write your report. All notebook data and report data will
be saved and sent to your teacher upon completion.
Understanding the Program
1. Start by ordering two wild type flies and mate them.
2. View your flies under the microscope and sort them.
3. View the flies close-up and note the difference between males and females.
4. Add your data to your notebook.
5. Use the computer to "analyze results"
6. Go to the chi square analysis. Enter your hypothesis. Since both of your parents with wild type, you
would expect a 50:50 ratio of male to females. You will need to use a calculator to determine the
expected numbers from the total number of offspring you have. Enter that number in the "hypothesis"
column.
7. The computer will do the chi square analysis for you and show your statistical results.
8. Return to your notebook and look at your data.
9. "Save" your notebook.
10. Click on the trash can on the lab bench and select “yes” when asked to clean out all previous
matings and start over. You must do this at the end of each assignment.
**Just play with the simulator for now to see what it does. Remove all your data from your notebook
before you start the real assignments.
*****Before you begin each assignment, make sure that you do not select traits that are lethal
and make sure that you only select traits from chromosome 1 if you are conducting a sex-linked
cross.
Assignment A: MONOHYBRID CROSS
Assignment A
(choose one of the following mutations)
Apterous
Black Body
Brown Eyes
Curved Wings
1. Choose ONE trait from the autosomal mutations on the table to study by ordering flies of the
mutant strain and crossing it with a wild type fly.
2. In the space below, construct two Punnett squares to predict the expected results of both parental
and F1 crosses. Name the trait you are testing.
Trait:
Parental Cross
F1 Cross
3. Refer to the Punnett Squares above. In the box below, record the expected and observed ratios
for the genotypes and phenotypes of the F1 and F2 offspring from the experiment.
Expected Genotypes and
Genotypic Ratio
Expected Phenotypes and
Phenotypic Ratio
F1
F2
Observed # of Each Phenotype
Observed Phenotypic Ratio
F1
F2
4. Cross your flies (P generation) and determine the phenotype of the F1 generation.
5. Mate the offspring (F1) from that cross together (creates F2 generation). Return to the lab and
choose "use fly in new mating" under the microscope view.
6. Sort your F2 flies and analyze results. You can choose to ignore sex here, since you know you
are studying only autosomal mutations.
7. Write a null hypothesis that applies to this genetic cross:
8. Run a chi square analysis on your F2 generation (again you can ignore sex) and record value.
9. Using the value from your chi-square analysis, discuss if you reject or fail to reject your null
hypothesis. Describe how chi-square analysis can be used to distinguish between the possible
inheritances of autosomal versus sex-linked traits.
Assignment B: SEX-LINKED TRAITS
1. A reciprocal cross is a wild type male x mutant female followed by a mutant male x wild type
female. (Obviously, you must study the same trait here). Choose an allele found on the sex
chromosome (chromosome I). [See attached chromosome map for sex linked alleles]
2. In the space below, construct two Punnett squares to predict the expected results of both sexlinked crosses. Name the trait you are testing.
wild-type male x mutant female (cross a)
mutant male x wild-type female (cross b)
3. Refer to the Punnett Squares above. In the box below, record the expected ratios for the
genotypes and phenotypes of the offspring from the experiment.
Expected Genotypes and
Genotypic Ratio
Expected Phenotypes and
Phenotypic Ratio
Cross a
Cross b
Observed # of Each Phenotype
Observed Phenotypic Ratio
Cross a
Cross b
4. Explain why there were no mutant offspring in cross b.
5. Using a male and female from the F1 generation of cross B, construct a Punnett square that
shows the F2 offspring and identify their expected genotypic and phenotypic ratios.
Punnett Square:
Expected Genotypes and
Genotypic Ratio
Expected Phenotypes and
Phenotypic Ratio
Assignment C: DIHYBRID CROSS
1. Select any two traits on two different chromosomes and study their inheritance patterns
(DIHYBRID CROSS) [See chromosome map]. Also be sure that you do not pick any traits that
are LETHAL as this will skew your data. (P generation: WT female, double mutant male).
2. In the space below, construct two Punnett squares (or one large Punnett square) to predict the
expected results of a dihybrid cross (F1 male x F1 female). Name the trait/s you are testing.
3. Cross an F1 offspring with another F1 offspring to generate an F2 generation. In the box below,
record the expected ratios for the phenotypes of the offspring from the experiment.
Traits
Expected Phenotypic Ratio
Observed # of Offspring
4. Test the expected ratio by performing a chi-square analysis and record value:
Assignment D: LINKAGE GROUPS
1. Select two traits on the same chromosome and study their inheritance patterns (excludes sexlinked and lethal mutations). [See chromosome map].
2. Cross a double mutant with a wild type. Choose traits that are less than 20 map units apart
on the same chromosome.
3. In the space below, construct two Punnett squares (or one large Punnett square) to predict the
expected results of the linked cross (F1 cross). Name the trait/s you are testing.
4. Refer to the Punnett Squares above. In the box below, record the expected number of offspring
for each phenotype (based on total # of offspring) from a typical dihybrid cross and the observed
number of offspring for each phenotype from the linked-trait cross.
Traits
Expected # (Unlinked
Dihybrid)
Observed # (Linked-trait)
5. Write a null hypothesis that addresses the difference between dihybrid crosses for genes on
different versus the same chromosomes.
6. Use the numbers in the table above to complete a chi-square analysis of the data. Show your
work below:
7. Based on your chi-square value, do you reject or fail to reject the null hypothesis?
8. Explain how a difference between expected and observed ratios of offspring from a dihybrid
cross can be used to determine if the traits are located near one another/are on the same
chromosome.
9. Determine what happens when you choose traits that are much farther apart by crossing
a new set of flies. Your results will vary due to the frequency of crossing-over.
10. Use your results from both parts of assignment D to calculate the recombination frequency of the
two crosses (less than 20 MU and more than 20 MU of separation). Use the recombination
frequency to calculate how far apart the traits are on the chromosome and discuss are close your
results are to what was given on the chromosome map.
Assignment E: LETHAL MUTATIONS
1. Choose a lethal allele and mate two flies that both have this allele.
2. Construct a Punnett square of the cross that you are testing.
Trait:
3. What are the phenotypes of the offspring and in what proportion? How does this differ from nonlethal alleles?
4. What is dominant (mutant or wild-type)? How can you tell from the cross?