BIOLOGY 103
      LAB 5:  VIRTUAL GENETICS 

 
 

THE EXPERIMENTS

For this lab you breed fruit flies to test hypotheses about how several different genes are inherited.  In earlier years, students in the class used real fruit flies to do this lab.  They would isolate P-1 females within a few hours of hatching (to make sure they were not already pregnant).  Then students would put the females in chambers with P-1 male fruit flies, homozygous for a particular allele.  After nearly two weeks, students would study newly-hatched F-1 flies and transfer them to new chambers to breed with mates selected for a particular experiment.   Now, thanks to our internet access, we can do "virtual" experiments, skipping all the waiting and the tedious microscopic examinations and sorting and counting of hundreds of offspring (assuming that the offspring or their parents hadn't died, ruining the experiment).  If you come to the real lab in WSB 206, we'll show you real fruit flies, just so you'll know what you're missing.  Or you could click to see Great Pictures of real fruit flies What we used to do: 

Turn in a report for your assigned mutation (do two if you work with a partner).  Your report (possibly co-authored) should follow the standard report form and MUST include all the information described in the six steps below. 

Use the Virtual FlyLab to test this hypothesis: "This mutation is recessive to the wild allele."   If you reject the hypothesis, you must devise and test an alternative hypothesis.   

If your report is co-authored, you will write about two mutations and you will test at least two hypotheses.

  1. Draw Punnett Squares of P-1 and F-1 crosses (classic monohybrid crosses).
  2. High-light the genotypes which would produce the mutant phenotype if your hypothesis is true.
  3. Write the hypothesis and predicted results (phenotype ratios of the F-1 and F-2 offspring).
  4. Have the Virtual FlyLab perform a P-1 and F-1 cross to test this hypothesis.  Step-by-step instructions of how to use the virtual lab are described in the example below, but feel free to wing it on your own.  If the Virtual FlyLab seems to be stuck somewhere, exit, then X out of NetScape or InternetExplorer and log on again.
  5. Record the results for both crosses; compare to the predicted results; make a conclusion (reject /  not reject).
    • If you do not reject this hypothesis, have the  Virtual FlyLab perform one more experiment, perhaps a test cross, to test the hypothesis again.   (Click the "new mate" button at bottom left if you never beamed down.)
    • If you do reject the original hypothesis, write a new hypothesis and show that it is consistent with the results of the first experiment. The best way to show that your new hypothesis explains the old results is to draw Punnett squares or to highlight the old Punnett squares with a different color.
  6. Do another experiment similar to steps #1-5 above but with new crosses using the same mutation:
    • Design an experiment with new crosses different from the first experiment the virtual lab performed
    • Draw new Punnett squares high-lighting the genotypes which would produce the mutant phenotypes
    • Write the new hypothesis and the predictions of the results of the new  and different experiment.
    • Beam up to the Virtual FlyLab to do the experiment.    (Click the "new mate" button at bottom left if you never beamed down.)
    • Write down the results and conclusion of the virtual lab experiment. Show that these results match the predictions deduced from the hypothesis
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Example: Ethel-Sue has been assigned the eye color mutation "white."

1. First, she writes the hypothesis, "White-eye is dominant to +." (+ is the conventional notation for the "wild-type" or normal or most common allele in fruit flies. You never know whether + is dominant or recessive or sex-linked or incompletely dominant or codominant. You simply know that it is the most common allele for this gene trait in wild fruit flies.)  Then Ethel-Sue makes two Punnett squares to show the genotypes for

  • The P-1 cross between the two pure-strain flies,   producing the F-1
    P-1 w w
    w+ w/w+ w/w+
    w+ w/w+ w/w+
  • The F-1 cross, where hybrids interbreed, producing the F-2 generation:
F-1 w w+
w w/w w/w+
w+ w/w+ w+/w+


2. Ethel-Sue highlights the genotypes which would produce white-eye phenotypes if her "white eyes are dominant" hypothesis is true:

  • The P-1 cross which produces the F-1
    P-1 w w
    w+ w/w+ w/w+
    w+ w/w+ w/w+
  • The F-1 cross which produces the F-2 generation:
    •
    F-1 w w+
    w w/w w/w+
    w+ w/w+ w+/w+

    3. Ethel-Sue writes her predicted results based on #1 and #2 above: If white is dominant to +, then in a classic monohybrid cross all the F-1 will have white eyes and 3/4 of the F-2 will have white eyes."

    4. Ethel-Sue beams up to the Virtual FlyLab. When it says "Log in to Use FlyLab" Ethel-Sue ENTERS THE USER ID AND PASSWORD WHICH WERE TAPED TO THE MONITOR.  Then she clicked  the "log in" box.  Ethel-Sue skips all the wordy part of the Virtual FlyLab; she immediately clicks the "start lab" button just above the "Introduction."  Then she clicks the proper buttons to make the P-1 cross.  

  • She clicks the design button under the picture of the lovely female fly.
  • She clicks the eye color mutations. The dots show that it is now set for "default," all wild type.
  • She clicks to change a dot for female "white."  Then she clicks the select button at the bottom.
  • The virtual lab returns her to the "mating page" and she clicks the design button under the picture of the handsome male fly.
  • Again she clicks the eye color mutations. The dots show that it is already set for "wild type," which is what she needs.  So she clicks the select button at the bottom.
  • The virtual lab returns her to the "mating page" and she clicks the mate button between the male and female.  (Don't click the "new mate" button at the lower right unless you have to start over completely.)
  • Magically, the offspring appear, right under the parents, labeled "Cross #1 Offspring."  Above each offspring picture is its sex, its PHENOtype, and how many babies (N) had this phenotype and sex.  At the top of the page she can still see the white-eyed mother and wild father
  • then the offspring (F-1), 497 female + and 498 male W. She writes this down, just in case.
  • For more information, Ethel-Sue clicks the analyze results button, getting a table which summarizes the F-1, even calculating ratios and proportions for her.
  • She clicks the add data to notebook button (upper right).
    •
  • Ethel-Sue decides to go ahead with the F-1 cross to produce the F-2 results.
  • She clicks return to lab (upper left) and then below the two offspring she clicks the two select buttons and then the mate button AT THE TOP (between the P-1 parents) (not the "new mate" button).
  • She that the page now shows some of the cross # 2 offspring (the F-2 generation).  By clicking the arrows near them, she can show
  • the rest of the cross #2 offspring (there are four fly types in this F-2)
  • or their parents (the F-1 generation)
  • She notes, by toggling the arrows,  these offspring (F-2): 249 female +, 252 male +, 246 female W, 250 male W. She writes this down.
  • Ethel-Sue then clicks the analyze results button, getting a table which summarizes the second cross offspring; then she clicks the add data to notebook button (upper right).
    •
  • Ethel-Sue clicks the export notes button, which gives her a new screen with all her results.  She electronically copies this page to an email she sends to herself because she forgot to bring a diskette.  However, she could just use the results she wrote down.
    •

    5. Ethel-Sue beams herself back to this planet and uses her biological brain to make sense of the results. Do they match the results predicted by the hypothesis? Oops. Good news! Ethel-Sue gets to reject the hypothesis. But…..oh no…..now she must figure out an alternative hypothesis. What kinds of genes could have produced these results???? Ethel-Sue decides skipping breakfast had been a mistake but now it's too late for Morrison and she forages for alternative energy sources in Jazzman Café and the bookstore and Common Grounds and unlocked rooms in South (finding bananas now containing fruitfly larvae) before settling into a higher trophic level in Albright  (left-over salami which contains housefly larvae). With energy surging into her brain, Ethel-Sue dashes back to her notes, accidentally tripping over two sophomores exploring other opportunities with each other. "Oh! " says Ethel-Sue. "Eureka! It's sex! My alternative hypothesis is that the white-eye mutation must be sex-linked and recessive."                                                            

    6. Ethel-Sue draws new Punnett squares to show what would happen if this alternative hypothesis is true: the white-eye mutation is sex-linked and recessive.

  • The P-1 mother has white eyes; the P-1 father is wild-type.  The male offspring are all white-eyed; the female offspring are all wild (red-eyed).
    P-1 Xw Xw
    Xw+ Xw/Xw+ Xw+/Xw
    Y Xw/Y Xw/Y
  • F-2 generation: half of the females have the wild phenotypes and half have the white-eyed phenotype, half of the males have the wild phenotypes and half have the white-eyed phenotype.
    •
    F-1 Xw+ Xw
    Xw Xw/Xw+ Xw/Xw
    Y Xw+/Y Xw/Y

    These Punnett squares do match the results of her first virtual experiment; so this new hypothesis can explain the results, but she needs stronger evidence. She designs another experiment. This time for the P-1 she will choose a wild female and a white-eyed male. Or maybe she will have the virtual fly lab perform a test cross between a white-eyed P-1 male and an F-1 female from her original experiment. No matter which experiment she chooses as a test for her new hypothesis, she must

    • Design an experiment with new crosses different from the first experiment the virtual lab performed
    • Draw new Punnett squares high-lighting the genotypes which would produce the mutant phenotypes
    • Write the new hypothesis and the predictions of the results of the new experiment.
    • Beam up to the Virtual FlyLab to do the experiment.  (Click new mate if you never beamed down.)
    • Write down or electronically copy the results of the virtual lab experiment. Show that these results match the predictions deduced from the hypothesis.                                                                   go back to top

    Mutations

    ASSIGNMENTS: Find your secret code  The number before your code assigns the mutation you must analyze.  Find the names for these mutations in the second column.  If you work with a partner, you must do both mutations.  Check with the instructor if you and your partner have been assigned the same mutation.
    •  6 --425   
    •  2 --1221
    •  20 --1223
    •  7 --2039
    •  18 --2160
    •  4 --2442
    •  14 --2467
    •  6 --3824
    •  12 --5215
    •  7 --5630
    •  13 --8560
    •  12 --9132
    •  13 --9681
    •  14 --90985
    •  14 --152805
    •  17 --281536
    •  17 --10s-piper
    •  20 --1112ae
    •  18 --1339d322
    •  20 --44 100
    •  18 --78577sbs
    •  20 --aaa
    •  22 --baby 18
    •  22 --bus21
    •  24 --c325
    •  24 --g0418a
    •  25 --gk1120
    •  25 --goz14
    •  6 --india
    •  2 --j3k63
    •  4 --jade 15
    •  7 ==jsb32113
    •  12 --laxin#9
    •  13 ==lucky 13
    •  25 ==lucy
    •  22 ==m115
    •  24 --oswald 18
    •  20 --perry
    •  25 --Petey
    •  18 --rootbean
    •  13 --sama
    •  24 --space toad
    •   12 --surfer 22
    •  
      •
    •  
    •  
    •  

    • x1 24  
      x2 25
      x3 20

     

     

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    		 Bristle Mutations
    1. forked
    2. shaven
    3. singed
    4. spineless
    5. stubble

    Body Color Mutations

    • 6. Black
    • 7. Ebony
    • 8. Sable
    • 9. Tan
    • 10. Yellow

    Antennae Mutations

  • 11. Aristapedia
    •

    Eye Color Mutations

  • 12. Brown
  • 13. purple
  • 14. sepia
  • 15. white
    •

    Eye Shape Mutations

    • 16. Bar
    • 17. eyeless
    • 18. lobe
    • 19. star

    Wing Size Mutations

    • 20. Apterous
    • 21. Miniature
    • 22. vestigial

    Wing Shape Mutations

    • 23. Curly
    • 24. Curved
    • 25. Dumpy
    • 26. scalloped

    Wing Vein Mutations

    • 27. crossveinless
    • 28. incomplete

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    Last updated 21 Sept 2002 
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