Genetics Problem Sets Worksheet With Answer Key Page 5
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14Genetics Problems Set #3
MULTIPLE ALLELES
The traits we have studied so far have had only two different alleles to express their
genotypes. Some traits have more than two alleles to express their genotype, these are
referred to as multiple allele traits. Human blood type (ABO factor) is an example.
In humans there are three alleles that influence blood type (ABO factor):
I A represents the "A" allele
I B represents the "B" allele
i
represents the "O" allele
Human blood types:
The symbols I A , I B , i, represent the three alleles that control the human ABO blood
group. The alleles I A and I B are codominant, and are both dominant to the i genotype.
The phenotypes are stated as blood types A, B, AB, and O.
Additional information (regarding a different protein one can identify in blood):
A separate gene causes the MN blood groups. The M and N alleles are codominant
(each causes its own antigen to be present in the blood). The genotypic expression of
this separate gene is as follows: M blood is MM, N blood is NN, and MN blood is MN.
1. List all possible genotypes for the human ABO blood groups, and indicate the phenotype for
each.
2. A man with blood type A marries a woman with blood type AB.
a. The couple has a son with blood type B. Show the genotypes of the parents and
the son.
b. Another couple with the same blood types has eleven children, but none of the
children has blood type B. What is the most likely explanation for this?
c. Could either of these couples have a child with blood type O? Explain your
answer.
3. Two newborn babies were accidentally mixed up in the hospital. Use the information given
to answer the questions that follow.
Baby 1: Type O
Mrs. Brown: Type B
Mrs. Smith: Type B
Baby 2: Type A
Mr. Brown: Type AB
Mr. Smith: Type B
Genetics Problems
5
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