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Name ________________________________ Class _______ Date _________________ Gene Linkage in Fruit Flies Use the virtual Genetics lab room to determine how the genes are linked in fruit fly chromosomes. Lab Bench Used Drosophila melanogaster, commonly known as the fruit fly, is a classic model organism for genetics research. In this virtual lab activity, you will investigate patterns of inheritance in different Drosophila traits, including some that are affected by gene linkage. Enter the Virtual Bio Lab and select the title of this lab activity from the “Heredity” menu on the whiteboard. You will be taken to the virtual Genetics lab room. Part A: Patterns of Inheritance In the Genetics lab, select the fruit fly (“Fly, Fruit”) in the Species Selector. Select “Body Color 1” as the trait to examine. First, cross a male that is homozygous for “Brown” with a female that is homozygous for “Ebony.” Make sure the “Include Male/Female” box in the lower left corner of the offspring results box is unchecked. 1. What body color phenotypes emerge in the F1 generation? Record the percentage of the offspring that display each phenotype. _____________________________________________________________ _____________________________________________________________ ____ 2. Click on “Next Generation.” Use “Generate Random Crosses” to produce the F2 generation from a random pairing from the F1 generation. Cross them enough times to produce 1000 offspring. What phenotypes show up in the F2 generation? What is the distribution of phenotypes? _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____ 3. Explain why “incomplete dominance” is an accurate name for the type of inheritance at work in these crosses. _____________________________________________________________ _____________________________________________________________ Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Virtual Bio Lab 1 Heredity: Gene Linkage in Fruit Flies Name ________________________________ Class _______ Date _________________ _____________________________________________________________ _____________________________________________________________ ________ Part B: Testing Mendel Reset the fruit fly experiment again. This time, select “Eye Color” as the trait and run a heterozygote-heterozygote cross enough times to produce 1000 offspring. 4. What is the pattern of inheritance for eye color trait? Provide evidence to support your conclusion. _____________________________________________________________ _____________________________________________________________ ____ ____________________________________________________________________ ____________________________________________________________________ 5. Reset the experiment and select “Eye Shape” as the trait. Again, run a heterozygoteheterozygote cross enough times to produce a sample size of 1000 offspring. What is the pattern of inheritance? Explain. _____________________________________________________________ _____________________________________________________________ ____ _____________________________________________________________ _____________________________________________________________ ____ 6. According to Mendel’s principle of independent assortment, the patterns of inheritance for two different traits should not affect each other. Use the two-factor Punnett square below to determine the results you would expect from a cross of fruit flies that are heterozygous for both traits, assuming Mendel’s principle holds true. R = red, r = white-sepia; B = bar, b = wildtype. Heterozygous Female (both traits) Heterozygous RB Rb rB rb Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Virtual Bio Lab 2 Heredity: Gene Linkage in Fruit Flies Name ________________________________ Class _______ Date _________________ Male (both traits) RB Rb rB rb Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Virtual Bio Lab 3 Heredity: Gene Linkage in Fruit Flies Name ________________________________ Class _______ Date _________________ 7. Based on the patterns of inheritance you determined in Questions 4 and 5, what is the expected phenotype ratio for the offspring? ____________________________________________________________________ ____________________________________________________________________ Set up the fruit fly experiment so that both eye color and eye shape are analyzed in the same cross. (To select two traits, hold the control or command button as you click on both traits in the list.) Set up the alleles so that both parents are heterozygous for both traits, as in the Punnett square above. Again, click “Cross” enough times to produce 1000 offspring. 8. Record the percentage of offspring that have each phenotype combination. (Hint: To convert decimals to percentages, multiply by 100.) ____________________________________________________________________ ____________________________________________________________________ 9. Convert the percentages to a ratio like the one in Question 7. (Hint: Find an approximate common factor for all four numbers, such as 3 or 5, and divide each percentage by that factor. Round the results to the nearest whole number.) _____________________________________________________________ _____________________________________________________________ ____ 10. How do the actual results of the virtual two-factor cross compare to your expected results from the two-factor Punnett square? Be specific in your description. _____________________________________________________________ _____________________________________________________________ ____ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ ________ Stop for a moment to think about why a fruit fly has two copies of its genes. Like other diploid organisms, it has two copies of every chromosome—one from its father, one from its mother. However, in order to reproduce, a fly needs to produce a gamete that has only one copy of every Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Virtual Bio Lab 4 Heredity: Gene Linkage in Fruit Flies Name ________________________________ Class _______ Date _________________ chromosome. Through meiosis, every gamete gets a mix of the fly’s mother’s and father’s chromosomes. Crossing-over between the homologous chromosomes makes the mix of genes in each gamete even more random. However, some genes are located very close together on a chromosome. During meiosis, unless a crossing-over event occurs right between the two genes, they will tend to be found together in the offspring. These are called linked genes. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Virtual Bio Lab 5 Heredity: Gene Linkage in Fruit Flies Name ________________________________ Class _______ Date _________________ 11. What combinations of eye color and eye shape alleles appeared more frequently than you expected in the F1 offspring? _____________________________________________________________ _____________________________________________________________ ____ 12. The genes for eye color and eye shape are linked, both located on the same chromosome in fruit flies. Why would the red-bar and white-sepia-wildtype allele combinations be more prevalent in the F1 generation than the other combinations? (Hint: Think about the parents’ chromosomes.) _____________________________________________________________ _____________________________________________________________ ____ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ _____________________________________________________________ ________ Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Virtual Bio Lab 6 Heredity: Gene Linkage in Fruit Flies