2. The allele for albinism (a) is recessive to the allele for normal pigmentation (A). A normally pigmented woman whose father is an albino marries an albino man whose parents are normal. They have three children, two normal and one albino. Give the genotypes for each person listed. Prove your answer
For each correctly conducted genetics problem, you receive 5 points for a maximum 20 points. All Punnett squares must
be shown.
1. There are 3 alleles controlling the ABO blood types. IA and IB are codominant genes so that the combination IAIB
produces the AB blood type. The third allele, (i) is recessive to the other two alleles. Show your work for each cross.
Indicate which of these parents could produce the given child.
The first one is provided with answers as an example.
(HINT: Do not forget that a heterozygous versus a homozygous blood type may yield different results. )
a)
Parent
A x AB
Child
IB
B
IA
IA
IA IA
IA IB
IA
IA IA
IA IB
IA
IB
IA
IA IA
IA IB
i
IA i
IB i
Produce Child of Type?
No
Produce Child of Type?
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b)
Parent
Child
A x O
A
Produce Child of Type?
Produce Child of Type?
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c)
Parent
Child
A x B
O
Produce Child of Type?
Produce Child of Type?
Produce Child of Type?
Produce Child of Type?
d)
Parent
Child
A x AB
O
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Produce Child of Type?
Produce Child of Type?
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e)
Parent
Child
B x B
O
Produce Child of Type?
Produce Child of Type?
Produce Child of Type?
f)
Parent
Child
AB x AB
A
Produce Child of Type?
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2. The allele for albinism (a) is recessive to the allele for normal pigmentation (A). A normally pigmented woman whose
father is an albino marries an albino man whose parents are normal. They have three children, two normal and one
albino. Give the genotypes for each person listed. Prove your answer.
8
Maternal Grandmother
Father
6
9
Maternal Grandfather
Mother
Child 1
8
7
Paternal Grandmother
5
6
Paternal Grandfather
7
5
4
1
4
3
Relationship
3
2
#
2
1
Child 2
9
Genotype(s)
Child 3
a) Show the cross of the paternal grandparents.
(HINT: What must their genotypes be to produce and albino child? )
b) What are the possible genotypes of the maternal grandmother?
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Show the cross of the mother and father.
3. In horses, black coat color is influenced by the dominant allele (B), and chestnut coat color by the recessive allele (b).
a) What color horse would you use to find out the genotype of a black trotter?
b) Give the genotype and phenotype. Show your work and discuss the reason you would know the genotype of the
black horse.
Possible Allele Pairings with Homozygous Dominant Trotter
F1 offspring probabilities:
Possible Allele Pairings with Heterozygous Trotter
F1 offspring probabilities:
Reasoning:
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4. In Drosophila, the fruit fly, white eyes are determined by a recessive Xlinked gene, and the wildtype or normal brick
red eyes are due to its dominant allele. Use symbols of the following types: X rY = a whiteeyed male; XRXR = a
homozygous normal red female.
a) What offspring can be expected from a cross of a whiteeyed male and a homozygous normal female?
b) Show the genotypes and list the phenotypes of the F1 offspring.
F1 Cross
F1 offspring probabilities:
Male
Female
RedEyed
WhiteEyed
c) Now, cross the F1 offspring. Show the genotypes and list the phenotypes of the F 2 offspring.
F2 Cross
F2 offspring probabilities:
Male
RedEyed
WhiteEyed
