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 sex-linked traits and test their
hypotheses by selecting fruit flies with different visible mutations, mating them, and
analyzing phenotypic ratios of the offspring.
Website: http://www.sciencecourswware.org/vcise/
Registration:
1. Create a new account
2. Class code (see your instructor)
3. Enter your first and last name (your username will be generated for you)
4. Choose your password. Make sure to write down your password and
username!
Notebook: The top tab contains a “notebook” link where you can enter data
gathered during your experiments. You will also want to write down important
information in a notebook that will be turned in at the end of the activity.
Understanding The Program
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Start by ordering two wild type flies and mate them.
View your flies under the microscope and sort them.
View the flies close-up and note the difference between males and females.
Add your data to your notebook.
Use the computer to “analyze results.”
Go to the chi square analysis. Enter your hypothesis. Since both of your
parents are wild type, you would expect a 50:50 ratio of males to females.
You will need a calculator to determine the expected numbers from the total
number of offspring you have. Enter the number into the “hypothesis”
column.
7. The computer will do the chi square analysis for you to show your statistical
results.
8. Return to your notebook and look at your data.
9. “Save” your notebook.
**Just play with the simulator for now to see what it does. You may want to clean
out your notebook after each assignment. Be sure to have some record of your
results and experiment.
Important: Check the Drosophila Chromosome map for lethal and sex-linked
traits.
Assignment A: MONOHYBRID CROSS
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. Cross your flies (P generation) and determine the phenotype of the F1
generation.
3. Now 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.
4. Sort your F2 flies and analyze results. You can choose to ignore sex here,
since you know you are studying autosomal mutations. Show that your
results follow a 3:1 ratio.
5. Run a Chi square analysis on your F2 flies (again you can ignore sex).
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 study the same trait here). Choose
an allele found on the sex chromosome. [See chromosome map for sex linked
alleles]
2. Show in your notebook how the offspring differ depending on which parent
had the mutant phenotype. Be prepared to explain why this happens in your
final lab report. You only need to look at the F1 generation here.
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.
a. Cross an F1 offspring with another F1 offspring to generate and F2
generation. This should demonstrate a 9:3:3:1 Mendelian ratio.
b. Test the 9:3:3:1 ratio by using the chi-square analysis.
Assignment D: LINKAGE GROUPS
1. Select two traits on the same chromosome and study their inheritance
patterns (exclude sex-linked 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.
3. What do you EXPECT from this cross? What are the observed outcomes?
What are the genotypes and phenotypes of your F1 generation? What are the
genotypes and phenotypes of your F2 generation? Do you observe any
crossing over (based on your outcomes)?
4. Determine what happens when you choose traits that are much further apart
by crossing a new set of flies. Your results will vary due to the frequency of
crossing over. Be able to explain these varied results on your lab report. Use
the F1 and F2 generation to determine how expected outcomes differ when
distant alleles are involved.
Assignment E: LETHAL MUTATIONS
1. Choose a lethal allele and mate two flies that both have this allele.
2. What are the phenotypes of the offspring and in what proportion? How does
this differ from non-lethal alleles?
3. What is the dominant (mutant or wild-type)? How can you tell from the
cross?
Final Report
Write a summary of what you discovered during this simulation.
Be sure to include:
An overview of the program (what did you do, why was this more efficient than
using live flies?).
Descriptions of each assignment and what your data showed.
Uncertainties that you have about what you saw in the activity.
Two new things you discovered while working through this simulation.
Plus, you will need to hand in any notes you kept during the simulation.