Going Past Mendel
Codominant Traits:
1. In cattle, the alleles for red coat and white coat are codominants. Both red and white hairs are produced so
that the heterozygote has a coat that is roan colored.
RR – red
RW – roan
WW – white
Make a punnett square crossing 2 cattle that are heterozygous.
a. What % of the offspring will have only red hair?
b. What % will have only white hair?
c. What % will be roan?
Incompletely Dominant Trait:
2. The factors for normal hemoglobin (A) and for sickle-cell hemoglobin (S) may be considered codominants.
A blood examination can detect the heterozygote, since a small percentage of the cells will show sickling.
A man whose cells show no sickling (AA) marries a healthy woman who is found to have a small percentage of
sickle cells (AS). (HINT: Make a punnett square.)
a. What is the chance of them having a baby with the severe sickle-cell?
The woman (AS) later marries a healthy man whose blood examination reveals sickle cells (AS).
(HINT: Make a punnett square)
b. What is the chance that their child will have the severe disorder?
c. What is the chance that one of their children is a carrier of the sickle cell allele?
3. In snapdragons the red and white colors are incompletely dominant creating a 3rd phenotype, pink.
Make a punnett square crossing a white flower with a red flower.
a. What are the chances of getting a white flower?
b. What are the chances of getting a red flower?
c. What are the chances of getting a pink flower?
Codominant and Multiple Allele Trait:
4. There are 3 subgroups blood. A, B and O. The allele A is codominant to B. A and B alleles are both
dominant to O.
a. What are the possible phenotypes for blood type? (HINT: You should have 4 answers.)
Make a punnett square of a male that has AB blood and a female that has O blood.
b.
c.
d.
e.
What are the chances of this couple having a child that has O blood?
What are the chances of this couple have a child with A blood?
What are the chances of this couple have a child with B blood?
What are the chances of this couple have a child with AB blood?