Name: ______Date: ______
Virtual Fly Lab
A Study in Mendelian Genetics
Objectives – The student will be able to:
A. Use the computer simulation to set up genetic crosses.
B. Analyze simulated data for the F1 and F2 generations of a monohybrid and dihybrid cross.
C. Recognize whether a trait is sex-linked or autosomal based on the offspring of a cross.
D. Perform a Chi-square statistical test to determine if the data are reasonably close to expected Punnett square ratios.
Logging in
1. Go to http://www.sciencecourseware.org/vcise/drosophila/ and click on “Create New Account”
2. Use the class code 8951543 and enter your first and last name.
3. Create your own username and password. Write it down here so you do not forget it.
a. User name ______
b. Password ______
4. Login. It sometimes takes a little while for the simulation to load. Be patient.
5. Never press the browser’s back button. You will lose your data and have to start over with your crosses.
Understanding the Program
1. Play around with the simulator to see how it works and what it does for each cross.
2. Start by ordering a wild-type female and a male with a different eye color. Add these to your Shopping Cart and Checkout.
3. Follow the on-screen instructions to set up the mating jar and putting it in the incubator.
4. Sort the flies into groups and click on each pile.
5. Add a male and a female fly from this first cross to a new mating jar (click “Use in New Mating”)
6. Return to the Lab and perform the new cross to obtain the F2 generation. Note: The simulation does not label the crosses P, F1, etc. for you, so you will need to keep track of which generation you are creating.
7. Sort the flies and determine if there is a difference in numbers of males and females in this generation of offspring.
a. If there is not a big difference between male and female offspring, you can combine these numbers in your data tables.
b. If there is a difference between the number of males and females of each phenotype, you may be dealing with a sex-linked trait and will need to separate the male phenotypes from the female phenotypes.
8. Back at the main lab bench, click on the trashcan and clear out previous matings to start fresh.
9. You can go back and look at previous crosses by clicking on the “Notebook” tab.
Assignment 1: Monohybrid Cross
1. Create a monohybrid cross by ordering and mating a wild-type female and a male fly with a black body. Black body is an autosomal recessive allele located on Chromosome II.
2. Record the numbers and phenotypes of the F1 offspring from this cross on the data sheet below.
3. Show the predicted Punnett square for the F1 cross on the data sheet.
4. Add a male and a female from this cross to a new mating jar and mate them to obtain the F2 generation.
5. Sort your F2 flies and record your results in the data area below. You can add the numbers of males and females for each phenotype together since this is an autosomal trait.
6. Demonstrate using a Chi-square analysis that your predicted F2 ratio was supported by the data. Use the following formula to calculate the Chi-square value. Compare this value to the critical values chart. Determine if the null hypothesis should be rejected (results do not match prediction) or not.
Monohybrid Cross
Parents’ Phenotype: ♀ (female): wild-type ♂ (male): black body (recessive)
Expected F2 results: Show the Punnett square for the cross between a male and female from the F1 generation. Write the expected phenotype fractions and ratio.
Question 1: Referring to the critical values chart, what is the p=0.05 probability value for these data? ______
Question 2: Based on your χ2 value, can you accept or reject your null hypothesis? Explain why.
Question 3: I told you that black body is an autosomal recessive allele. How is this supported by the data from the crosses you just performed?
Assignment 2: Dihybrid cross
1. Design a dihybrid cross by ordering an ebony body female fly and a male fly that has the vestigial mutation for wing size. Add these flies to your shopping cart and checkout.
2. Predict the results of the cross by drawing out the Punnett squares for both F1 and F2 in the data area below.
3. Perform the first cross, sort the flies and record the phenotypes and numbers of actual F1 offspring.
4. Add the F1 female and an F1 male to a new mating jar and perform the F2 cross.
5. Sort the flies and record the actual F2 offspring phenotypes and numbers in the data area below. If the number of females and males for all phenotypes are approximately equal, you can add male and female offspring together under one phenotype.
6. Analyze the results of the F2 cross by doing a Chi-square analysis. Compare the Chi-square value to the critical values chart for the correct number of degrees of freedom. Determine if the null hypothesis should be rejected (results do not match prediction) or not.
Dihybrid Cross
Parents’ Phenotype: ♀ (female): ______♂ (male): ______
Parents’ Genotype: ♀ (female): ______♂ (male): ______
Expected F1 and F2 results: Complete the Punnett squares for both F1 and F2 crosses. Write the cross and expected phenotype fractions and ratios for each.
F1 Cross Phenotypes: ♀ (female): ______♂ (male): ______
Question 4: How many degrees of freedom would you use? ______What is the p=0.05 critical value? ______
Question 5: Based on your χ2 value, can you accept or reject the null hypothesis? Explain why.
Question 6: Are the ebony body and vestigial alleles autosomal traits or sex-linked traits? How did the data support your answer?
Assignment 3: Sex-Linked Cross
1. Order a female fly with a tan colored body with a wild-type male. Add to your shopping cart and checkout.
2. Predict the results of the cross by drawing out the Punnett squares for both F1 and F2 in the data area below.
3. Perform the cross, sort the flies and record the phenotypes and numbers of actual F1 offspring.
4. Add the F1 female and an F1 male to a new mating jar and perform the F2 cross.
5. Sort the flies and record the actual F2 offspring phenotypes and numbers in the data area below.
6. Analyze the results of the F2 cross by doing a Chi-square analysis. Determine if the null hypothesis should be rejected (results do not match prediction) or not.
Sex-Linked Cross
Parents’ Phenotype: ♀ (female): ______♂ (male): ______
Parents’ Genotype: ♀ (female): ______♂ (male): ______
Expected F1 and F2 results: Show the Punnett squares for F1 and F2 crosses. Write the cross and the expected. Write the expected phenotype fractions and ratios for each.
F1 Cross Phenotypes: ♀ (female): ______♂ (male): ______
Question 7: Based on the χ2 value, can you accept or reject your null hypothesis? Explain why.
Question 8: Explain how the results of the crosses demonstrate that the tan body allele is sex-linked.
Check for Understanding Conclusion questions
1. Suppose you were to obtain a Chi-square value of 7.82 or greater in your data analysis (with 2 degrees of freedom). What would this indicate?
2. Suppose you were to obtain a Chi-square value of 4.60 or lower in your data analysis (with 2 degrees of freedom). What would this indicate?
3. A heterozygous white-fruited squash plant is crossed with a yellow-fruited plant, yielding 200 seeds. Of these, 110 produce white-fruited plants while only 90 produce yellow-fruited plants. Are these results statistically significant? Explain using Chi-square analysis. Show your work, including Punnett square predictions. What if there were 2000 seeds and 1100 produced white-fruited plants and 900 yellow-fruited?
4. A wild-type fruit fly (heterozygous for gray body color and red eyes) is mated with a black fruit fly with purple eyes. The offspring are wild-type, 721; black-purple, 751; gray-purple, 49; black-red, 45. What is the recombination frequency between these genes for body color and eye color?