Name: ______Date: ______

Assignment 2: Dihybrid Cross (ebony body and vestigial wing)

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Once you are comfortable with using Science Courseware to perform a monohybrid cross, design a dihybrid cross by selecting and crossing an ebony body female fly with a male fly that has the vestigial mutation for wing size.

1.Parental Cross

Generation / Phenotype and Genotype of ♀ / x / Phenotype and Genotype of ♂
Body color / Wing size / Body color / Wing size
P / x
  1. Fill in the expected proportions of the phenotypes of F1 generation in the table. Show your work (use a Punnett square or the basic rules of probability). I have provided a list of possible genotypes.

Circle the genotype that matches the offspring from this cross.
+/+; +/+
+/+; +/E
+/VG; +/+
+/VG; +/E

Show work, here.

Phenotype and Symbol of the offspring from #2 / Expected Proportion or Ratio
of the F1 generation
+ (wild-type)
E (ebony body)
VG (vestigial wing)
VG;E (vestigial wing and ebony body)
  1. Fill in the observed numbers of each phenotype produced in this cross. Determine the proportions of the cross and fill them in. Choose “ignore sex” in your analysis.

F1 generation: Observed Proportions

Phenotype and Symbol / Observed #s / Observed Proportions or Ratios
+ (wild-type)
E (ebony body)
VG (vestigial wing)
VG;E (vestigial wing and ebony body)
  1. Does it appear that your prediction was supported?

5.F1 Cross. Cross a male and a female from the F1 generation to produce the F2 Generation.Fill in the phenotypes and genotypes of the individuals in this cross.

Generation / Phenotype and Genotype of ♀ / x / Phenotype and Genotype of ♂
F1 / x
  1. In the space below, list the expected proportions of the phenotypes of the F2 generation. Use your notes to determine this.

Phenotype / Expected Proportion or Ratio of the F2 generation
+ (wild-type)
E (ebony body)
VG (vestigial wing)
VG;E (vestigial wing and ebony body)
  1. Test of the hypothesis.
  2. Choose “Send Data to Computer”
  3. Choose “Analyze Results”
  4. Choose “Ignore Sex”
  5. Fill in the observed numbers of each phenotype produced in this cross. Determine the proportions of the cross and fill them in.

F2 Generation Data

Phenotype and Symbol / Observed #s / Observed Proportions or Ratios
+ (wild-type)
E (ebony body)
VG (vestigial wing)
VG;E (vestigial wing and ebony body)
  1. Calculate the expected numbers of each phenotype and enter them in the table below.The expected value equals the total # times the expected proportion.
  1. Χ2Test

Phenotype / # Observed / # Expected / O – E / (O – E)2 / (O – E)2 / E
total
Χ2 =
  1. How many degrees of freedom (df) are there? ______
  1. Was your Ho accepted or rejected? Explain how you came to this conclusion.

We will now check our answer against the one calculated by the program

  1. Click on the “Chi Square Analysis” button.
  2. Enter your predicted ratio in the table (whole numbers only). You may enter the % phenotypes that you calculated in #2.
  3. Select “test this hypothesis.”
  4. Did the computer calculation match yours?
  1. Which alleles are dominant? ______
  1. Which alleles are recessive?
  1. Are these genes autosomal or X-linked? Explain your reasoning.

df / P = 0.05
1 / 3.84
2 / 5.99
3 / 7.82
4 / 9.49