AP Biology Advanced Genetic Problems 4-11-13
Codominance/Incomplete Dominance
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Complete all crosses using and superscript notation for blood type and other codominant
traits.
Codominant alleles are notated with a capital initial and superscript. (ex: IAIB for AB
blood type) recessive alleles are written as the lowercase initial (ex: ii for O blood type)
1. Mom has type A blood. Dad has type AB blood. What possible blood types could their
children inherit? (Show all possibilities).
2. Mom has type O blood. Dad has type AB blood. What percentage of their kids will inherit
type B blood?
3. Mom has type B blood. Dad has type O blood. They have a child with type O blood. Make
a punnett square to show what Mom’s genotype must be to have a child with type O blood.
4. A woman sues a man for child support, claiming that he is the father of her illegitimate child.
The woman is type A, the child is type O, and the man is type AB. Could he be the father of
her child? Show why or why not.
5. A wealthy elderly couple dies together in an accident. A man comes forward, claiming that
he is their long lost son and is entitled to their fortune. The couple were of blood types AB
and O. The man has type O blood. Could he be the heir to the fortune? Show why or why
not.
6. John has type O blood. He knows his mother had type B blood. He does not know the
identity of his father, however. What possible blood types could his father have had? Show
your work.
7. Mike has type AB blood. Paul has type O blood. Mike knows that his Mom had type B
blood. Show how it could be possible for Mike and Paul to be brothers.
8. Mom’s genotype is IAi and she is Rh negative. Dad’s genotype is IA IB and he is
heterozygous for the Rh factor. Use a dihybrd cross to show the inheritance of blood type in
their children.
9. You can use the same notation we see in blood type for other codominant traits as well. In
cows, the red and white coat color alleles are codominant. We can choose an initial to
represent this trait, like “C” for coat. Then we can give the codominant alleles superscripts.
Show a cross between a white cow (CWCW) and a red cow (CRCR)
Note: When selecting an initial to represent a codominant trait, do not use X, Y, or I. X & Y are
specific to sex chromosome inheritance and I is specific to blood type.
10. In chickens, black and white feather color are codominant alleles for this trait. Using
superscript notation, show a cross between two black and white feathered chickens
(erminette).
Sex-linked Traits Practice Problems
11. In fruit flies, the gene for white eyes is sex-linked recessive. (R) is red and (r) is white. Cross
a white-eyed female with a normal red-eyed male.
a. What percent of the males will have red eyes? White eyes?
b. What percent of the females will have red eyes? White eyes?
c. What percent of the offspring will be white-eyed?
d. What percent of the offspring will be carriers of the white eye trait?
12. Using the same information as for question #1, cross a heterozygous red-eyed female with a
red-eyed male.
a. What are the genotypes of each parent?
b. What fraction of the children will have red eyes?
c. What fraction of the children will have white eyes?
d. What fraction of the female children will carry the white eyed trait?
13. In humans, hemophilia is a sex-linked recessive trait. If a female who is a carrier for
hemophilia marries a male with normal blood clotting, answer the following questions.
a. What fraction of the female children will have hemophilia?
b. What fraction of the female children will be carriers?
c. What fraction of the male children will have normal blood clotting?
d. What fraction of the male children will be carriers?
e. What fraction of the male children will have hemophilia?
14. Two normal visioned parents have a color-blind son. Give the genotype of both parents and
the son.
15. In cats, the allele (B) produces black color but (b) produces a yellow color. These alleles are
incompletely dominant to each other. A heterozygote produces a tortoise shell color. The
alleles (B) and (b) are sex-linked as well. Cross a tortoise shell female with a yellow male.
a. What percent of their offspring will be yellow?
b. What percent of their offspring will be black?
c. What percent of their offspring will be tortoise shell?
d. Why is it impossible to have a tortoise shell male offspring?