Multiple Alleles
All traits discussed so far have been controlled by a single pair of alleles. However, there are some traits, such as
human blood type that involved more than 2 alleles. Human blood type involves three alleles: IA , IB, and і. Genes
IA and IB are dominant while і is recessive. The 4 blood types produced by these 3 alleles are A, B, AB and O.
Genotypes of multiple alleles are shown using the capital letter I for dominant and lower case і for recessive. For
example, type A blood genotype is IAIA.
Questions:
1. In humans, an example of a trait cause by multiple alleles would be
.
2. In the human population, there exist
alleles for blood type. But an individual only has
alleles for blood type. From these alleles, how many blood types are produced? _____
___
3. Give the genotypes for the following blood types:
Type A
or
Type AB
Type B
or
Type O
4. A man with blood type AB marries a woman with type O blood. Using the Punnett Square below, show all
possible genotypes of their offspring.
5. Could a mother with type B blood and a father with type O blood produce offspring with type AB blood? Show a
Punnett Square below to check your answer.
6. In a paternity case, a woman (blood type O) claims a man (type A) whose mother is O to be the father of her
child. Is there any possibility the woman is correct? If so, show the genotypes of the people involved and a likely
cross to produce a child with blood type O.
7. A woman who is homozygous for blood type A marries a man who is heterozygous for blood type B. What
possible blood types could their children have? Show the cross.
8. Jill is blood Type O. She has two older brothers (who tease her like crazy) with blood types A & B. What are the
genotypes of her parents with respect to this trait?
9. A test was done to determine the biological father of a child. The child's blood Type is A and the mother's is B.
Dude #1 has a blood type of O, & dude #2 has blood type AB. Which dude is the biological father?
10. A man with Type O blood marries a woman with heterozygous Type A blood. What are the possible
phenotypes of the children?
On a certain day in a local hospital, two male babies were born. After the mothers returned home with their
infants, Mrs. Robinson discovered a tag marked “K” on her baby. The other mother, Mrs. Koffer, insisted she had
her own baby and refused to exchange. The matter came to court where all agreed to submit to blood test. Here
are the results:
Mrs. Robinson – Type O
Mrs. Koffer – Type O
Mr. Robinson – Type O
Mr. Koffer – Type AB
Baby taken home by the Robinsons – Type A
Baby taken home by the Koffers – Type O
12. Did a switch occur? Explain using Punnett Squares to support your answer
Human hair color is controlled by one gene with four alleles (with some incomplete dominance)
HBr = brown
HBd = blonde
hR = red
hbk = black
The possible genotypes and phenotypes:
HBdHBd or HBd hbk = blonde
HBd HBr = mousy brown
Bd R
H h = strawberry blonde
HBr HBr or HBr hbk = brown
Br R
H h = auburn
hR hR or hR hbk = red
hbk hbk = black
13. If someone with auburn hair has children with someone with red hair (but whose mother had black hair), what
are the genotype and phenotype probabilities for their children?
14. If someone with red hair has children with someone with auburn hair, what are the genotypic and phenotypic
probabilities for their children?