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• Experiment 6 Exercise 1 – Monhybrid Crosses
• Experiment 6 Exercise 2 – Dihybrid Cross
• Experiment 6 Exercise 3 – Inheritance of Human Traits

Experiment 6 Exercise 1: Monohybrid Crosses

You will be conducting monohybrid crosses using fruit flies. Open in the following website:

Glencoe-McGraw Hill. No date. Punnett Squares


A. Open the above website and click on the VCR to listen to the introduction. Close the window when done.

B. Click on the Lab Notebook on the lab bench. A breeding scenario will be presented to you that you will need to carry out. Here are the possible phenotypes and genotypes you will using:

a. Normal wings (LL or Ll) or vestigial wings (ll)
b. Gray body (GG or Gg) or black body (gg)
C. Enter the Scenario number in Table 1 below.

D. Based on the Scenario, use the down arrows beneath the Parent 1 and Parent 2 boxes to select the appropriate parents. Look carefully at the flies so that you know which ones to select.

E. Before proceeding, click on the Check Parents button. If necessary, make corrections. If you are correct, the maternal and paternal alleles will be aIDed to the Punnett Square.

F. Next, drag the correct allele combinations and the corresponding fly types to the boxes in the Punnett Square.

G. When you are done, click on Check Offspring. If necessary, make corrections.

H. Record your data in Table 1 below. An example has been given, but note that the example is not using the genotypes and phenotypes used in this exercise.

I. Click on Reset. Repeat steps B – H four more times for a total of five crosses. If a scenario is presented that has already been completed, click Reset again. DO NOT REPEAT a given scenario!

Note that the scenario number you need to record in the Table below is the number associated with the specific scenario you completed.

Table 1. Results of crosses.


Parent Genotypes

Offspring Genotypes

Offspring Phenotype

Scenario #

Parent 1

Parent 2








2 Rr
2 rr

50% Rr
50% rr

2 red
2 white

50% red
50% white





































1. Which type of cross gave you the greatest number of genotypes? Was the number of phenotypes the same as the number of genotypes or different? If different, why?

2. Can the genotype for a gray-bodied fly be determined? If so, how??

Experiment 6 Exercise 2: Dihybrid Cross

We will continue to use flies for our crosses, but this time we will examine the inheritance of TWO different traits: body color (gray or black) and wing type (long or vestigial). As with our first crosses, the gray body color is dominant (GG or Gg) over the black body color (gg). And the long wing type is dominant (LL or Ll) over vestigial (ll). Be sure you have reviewed our online Genetics lecture and this week’s reading before proceeding. An example of a dihybrid cross is shown on p 150 in your book.

Recall our flies from the previous exercise. We have the following traits:

• Gray body (GG or Gg) is dominant over black body (gg)
• Long wings (LL or Li) is dominant over vestigial wings (ll)

We will cross a gray bodied fly with long wings which has the genotype GGLl with a gray bodied fly with long wings with a genotype of GgLl . Note that even though the phenotypes are the same, the genotypes of the two parents are different.

Identify the four possible gametes produced by these two individuals. Note that each gamete must consist of two alleles (G or g and L or l):

Parent 1 Parent 2

Parent 1 (GGLl) Gametes: _______ ______ _______ _______

Parent 2 (GgLl) Gametes: _______ ______ _______ _______

Create a Punnett square to show the outcome of a cross between these two individuals (GGLl and GgLl) using the gametes you identified above.



Parent 1







Parent 2

























1. What are the possible F1 genotypes (these must now have four alleles) and their percentages?

2. Recall that GG and Gg individuals are gray bodied, while gg individuals are black bodied and that LL and Li individuals have long wings, while ll individuals have vestigial wings. What are the phenotypes of the resulting offspring and what are the percentages of these phenotypes?

Experiment 6 Exercise 3: Inheritance of Human Traits

Read over the Inheritance of Human Traits Introduction under the Week 6 Experiment link in our course before beginning.


A. For each of the heritable traits describe below, determine which form you have (dominant form or recessive form). This is your phenotype.

B. Record your phenotype information in Table 2 below. Then, enter the possible genotype(s) you have based on your phenotype.

C. Answer the questions found following Table 2 below.

Description of Heritable Traits

An example is shown as to what should be entered in RED. Please correct the entry for “Ear lobes” based on your personal data. For the Genotypes, please use the letters provided above (8 pts).

Table 2. Your phenotypes and genotypes.




Ear lobes

Unattached OR Detached





Tongue Rolling



Hand Folding






Tongue Folding






Little Finger



Mid-digital Hair




1. Which traits did you have that were dominant?

2. Which traits did you have that were recessive?

3. What does it mean to be homozygous for a trait? Cite source(s) used.

4. What does it mean to be heterozygous for a trait? Cite source(s) used.

5. Define genotype and phenotype? Cite source(s) used.

6. Which traits do you know for sure that you were homozygous?

1. Marfan syndrome follows a pattern of autosomal dominant inheritance. What is the chance (= probability) that any child will inherit the dominant allele if one parent (Parent #1) does not carry the allele and the other (Parent #2) is heterozygous for it? Provide a clear explanation and complete the Punnett Square below. Be sure to define the letters you use for the two alleles and what the genotypes are of each parent.

2. Below is a diagram showing the inheritance of an X-linked trait; the first generation is at the top and the third generation is at the bottom. Describe what this pedigree depicts in terms of gender, presence or absence of the disorder, and what feature(s) indicate that the pedigree is for an X-linked trait.

3. In one experiment, Mendel crossed a pea plant that bred true for green pods with one that bred true for yellow pods. All of the F1 plants had green pods. What does it mean when an organism like Mendel’s pea plants is true breeding? Which form of the trait (green or yellow pods) is dominant? Explain how you arrived at your conclusion. This should include the possible genotypes of the parents involved in the cross and those of the F1 generation.

4. What type of mutation has occurred in the DNA of people with sickle cell anemia? (Look back, if you need to, to see what causes sickle cell.)

5. A man who has type B blood and a woman who has type A blood could have children of which phenotypes? Explain your answer; be sure to consider what the possible genotypes are for both parents in your answer.

6. Unattached earlobes are a dominant trait. If A denotes the allele for unattached earlobes, and a denotes the allele for attached earlobes, what is (are) the possible genotype(s) of a person who has unattached earlobes?

Could both parents of a person with unattached earlobes have attached earlobes? Why or why not? Think about what the parent’s genotypes have to be.

7. How are a locus, allele and a gene similar? How would you differentiate among these three terms?

8. Explain what is meant by polygenic inheritance, pleiotropy, and human gene therapy. Provide an example of each.

Attachment:- Experiment_Answer_Sheet.rar


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