Guided Practice Problem #1
Complete Dominance
Rolling your tongue is a genetic trait inherited from his or her parents. The ability to roll the tongue is
expressed by a dominant trait. Your friend’s parents are heterozygous for rolling their tongues. Answer the
following questions about the parents and possible offspring.
1. What is the trait being studied in this scenario? ____________________________________________
2. Indicate the dominant and recessive genes and assign an appropriate letter to each allele:
a. _____________________________________________________
b. ____________________________________________________
3. What is the genotype of Parent #1 (mother)? Use both ways to express the genotype: letters and the
scientific term. ________________________ ______________________________________________
4. What is the genotype of Parent #2 (father)? Use both ways to express the genotype: letters and the
scientific term. _______________________________________________________________________
5. What is the phenotype of Parent #1 (mother)? _____________________________________________
6. What is the phenotype of Parent #2 (father)? ______________________________________________
7. Draw a Punnett Square to represent the offspring the parents above are likely to have.
8. What are the possible genotypes of the offspring? __________________________________________
9. What are the possible phenotypes of the offspring? _________________________________________
10. What is the probability that the offspring will have a homozygous dominant genotype? ____________
11. What is the probability that the offspring will have a heterozygous genotype? ____________________
12. What is the probability that the offspring will have a homozygous recessive genotype? _____________
13. What is the genotype ratio for the possible offspring? _______________________________________
14. What is the probability that the offspring will have a phenotype of a rolling tongue? _______________
15. What is the probability that the offspring will have a phenotype of no rolling tongue? ______________
16. What is the phenotype ratio for the possible offspring? ______________________________________
17. What is the probability that your friend will be able to roll his/her tongue? ______________________
Guided Practice Problem #2
Complete Dominance
Complete the following questions if you bought a pair of pea plants on sale at the local nursery. The clerk at
the store told you that the tall stemmed pea plant’s genotype is homozygous dominant. The other plant’s
genotype is homozygous recessive and has a short stems.
1. What is the trait being studied in this scenario? ____________________________________________
2. Indicate the dominant and recessive genes and assign an appropriate letter to each allele:
a. _____________________________________________________
b. ____________________________________________________
3. What is the genotype of Parent #1 (mother)? Use both ways to express the genotype: letters and the
scientific term. ________________________ ______________________________________________
4. What is the genotype of Parent #2 (father)? Use both ways to express the genotype: letters and the
scientific term. _______________________________________________________________________
5. What is the phenotype of Parent #1 (mother)? _____________________________________________
6. What is the phenotype of Parent #2 (father)? ______________________________________________
7. Draw a Punnett Square that represents the possible offspring.
8. What are the possible genotypes of the offspring? __________________________________________
9. What are the possible phenotypes of the offspring? _________________________________________
10. What is the probability that the offspring will have a homozygous dominant genotype? ____________
11. What is the probability that the offspring will have a heterozygous genotype? ____________________
12. What is the probability that the offspring will have a homozygous recessive genotype? _____________
13. What is the genotype ratio for the possible offspring? _______________________________________
14. What is the probability that the offspring will have a tall height phenotype? ___________________
15. What is the probability that the offspring will have a short height phenotype? __________________
16. What is the phenotype ration for the possible offspring? _____________________________________
17. If you wanted to produce more short pea plants rather than tall pea plants, would you be able to with
these two plants? _____________________________ Explain why on the back of this sheet of paper.
Guided Practice Problem #3
Complete Dominance
A white flowered plant is crossed with a plant that is heterozygous for purple flowers. Purple flowered
plants have at least one dominant allele, while white flowered plants have no dominant alleles. Answer the
following questions for this cross.
1. What is the trait being studied in this scenario? ____________________________________________
2. Indicate the dominant and recessive genes and assign an appropriate letter to each allele:
a. _____________________________________________________
b. ____________________________________________________
3. What is the genotype of Parent #1 (mother)? Use both ways to express the genotype: letters and the
scientific term. ________________________ ______________________________________________
4. What is the genotype of Parent #2 (father)? Use both ways to express the genotype: letters and the
scientific term. _______________________________________________________________________
5. What is the phenotype of Parent #1 (mother)? _____________________________________________
6. What is the phenotype of Parent #2 (father)? ______________________________________________
7. Draw a Punnett Square to demonstrate the cross in the scenario above.
8. What are the possible genotypes of the offspring? __________________________________________
9. What are the possible phenotypes of the offspring? _________________________________________
10. What is the probability that the offspring will have a homozygous dominant genotype? ____________
11. What is the probability that the offspring will have a heterozygous genotype? ____________________
12. What is the probability that the offspring will have a homozygous recessive genotype? _____________
13. What is the genotype ratio for the possible offspring? _______________________________________
14. What is the probability that the offspring will have a phenotype of purple flowers? ________________
15. What is the probability that the offspring will have a phenotype of white flowers? _________________
16. What is the phenotype ration for the possible offspring? _____________________________________
17. You want to have a pea plant garden with about fifty percent white and fifty percent purple flowers.
Which offspring would you cross to ensure that you would keep producing about half of each flower
color every generation? _________________________________
a. Create more Punnett Squares to help you answer this question on the back of this sheet.
b. Explain you answer on the back of this sheet.