Download Monohybrid Practice

Monohybrid Crosses Notes
Monohybrid Crosses: A breeding used to illustrate the inheritance of one genetic trait
The following is a simplified example, as many traits are determined by more than one gene.
Trait being followed:
Dominant allele is represented by
and the dominant phenotype is
Recessive allele is represented by
and the recessive phenotype is
.
.
Homozygous – Homozygous Crosses
1. Cross homozygous dominant (
) with homozygous dominant (
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
2. Cross homozygous recessive (
) with homozygous recessive (
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
3. Cross homozygous dominant (
) with homozygous recessive (
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
):
):
):
Homozygous – Heterozygous Crosses
4. Cross homozygous dominant (
) with heterozygous (
):
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
5. Cross homozygous recessive (
) with heterozygous (
):
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
Heterozygous – Heterozygous Cross
6. Cross heterozygous (
) with heterozygous (
):
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
Name: _______________________
Monohybrid Crosses Application
Period: ______________________
Suppose you work for a company that sells plant seeds. You are studying a plant species in which the dominant
phenotype is pink flowers (genotypes PP or Pp). The recessive phenotype is white flowers (genotype pp).
1.
If you currently have one homozygous recessive plant (genotype =
one homozygous dominant plant (genotype =
),
) and one heterozygous plant (genotype =
),
which two plants should you breed together to get the highest % of offspring with the recessive phenotype?
Hint: Check the results from the crosses on the previous worksheet.
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
2. Now you have only the offspring of the cross to breed together.
Which offspring should you crossbreed to get the highest % with the recessive phenotype in the 3rd generation?
Offspring possibility #1 genotype:
phenotype:
Offspring possibility #2 genotype:
phenotype:
Offspring possibility #3 genotype:
phenotype:
Offspring possibility #4 genotype:
phenotype:
% Homozygous dominant offspring:
phenotype:
% Homozygous recessive offspring:
phenotype:
% Heterozygous offspring:
phenotype:
Application #3:
Customers have been requesting more plants with pink flowers. To meet this demand, you need to
determine the genotypes of some of the plants you have been studying.
You are presented with Plant A of this species. Plant A has pink flowers.
What are the possible genotypes of Plant A? ______ or ______
You cross Plant A with Plant B, which has white flowers. What is the genotype of Plant B? ______
Crossing Plant A with Plant B results in 6 plants with pink flowers and 6 plants with white flowers.
Use the two Punnett squares to determine the genotype of Plant A.
a. What is the genotype of Plant A? Explain how you arrived at your answer.
b. What are the possible genotypes and phenotypes of offspring if Plant A is crossed
with a plant that has a genotype of PP?
c. What ratio of dominant to recessive phenotypes would exist if Plant A was crossed
with a plant with a genotype of Pp? Draw your own Punnett square if you like.
d. Is Plant A the best plant, in terms of genotype, that you can work with to produce as many seeds
for pink plants as possible? Explain why or why not. If not, explain which genotype would be best.