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Name _______________KEY_______________
Biology 201 (Genetics)
Exam #1
29 September 2003
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Read the question carefully before answering. Think before you write. Be concise.
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You will have up to one hour to take this exam. After that, you MUST stop no matter
where you are in the exam.
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If I can not read your handwriting, I will count the question wrong.
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Use clear gene symbols (i.e. Aa is easier to distinguish that Oo).
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Sign the honor pledge if applicable.
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Good luck!
I pledge that I have neither given nor received unauthorized assistance during the completion
of this work.
Signature: __________________________________________________________
1. Species 847 (an extraterrestrial being) has 40 chromosomes per diploid cell. In this
organism, sex determination is via the XX/XY mode.
a. How many chromosomes does a species 847 child receive from its father? _20___
b. How many autosomes are present per diploid cell? ___38_____
c. How many autosomes are present in a haploid sperm? ___19____
d. How many sex chromosomes are present in a haploid egg? ___1____
2. Consider the pedigree below of a human disease controlled by one gene. Indicate all
possible modes on inheritance of the disease trait that are consistent with the pedigree.
For each possible mode of inheritance, indicate the genotypes of the individuals, making
sure that you provide a legend.
I-1
II-1
I-2
II-2
mode
legend
autosomal
A- = disease
dominant
aa = no disease
autosomal
A- = no disease
recessive
aa = disease
X-linked XA - = no disease
recessive Xa Xa or XaY = disease
II-3
II-4
I-1
Aa
I-2
aa
II-1
aa
II-2
Aa
II-3
aa
II-4
Aa
aa
Aa
Aa
aa
Aa
aa
XaY
XA Xa
XAY Xa Xa
XA Xa
XaY
3. In garden peas, tall stem (T) is dominant over short stem (t),
green pods (G) are dominant over yellow pods (g)
smooth seeds (A) are dominant over wrinkled seeds (a)
Suppose a homozygous short, green, wrinkled pea plant is crossed with a homozygous
tall, yellow, smooth one.
a. What will be the appearance of the F1? tall stem, green pods, smooth seeds
b. If the F1s are interbred, what proportion of the F2 progeny will be homozygous
dominant or all three characters or homozygous recessive for all three characters?
=Probability(TTGGAA) + Probability(ttggaa)
(¼*¼*¼) + (¼*¼*¼) = 1/32
c. If the F1s are interbred, what proportion of the F2 progeny will look like the F1
generation?
F1 generation was tall stem, green pods, smooth seeds
= Probability(T-G-A-)
(3/4 * 3/4 * 3/4) = 27/64
4. A homozygous yellow petal plant is crossed with a homozygous purple petal plant. The
F1 plants are purple. The F1 plants are crossed with each other. The result of this cross
was 118 purple petal plants and 90 yellow petal plants.
a. Based on these data, provide the mode of inheritance of petal color in this plant.
Duplicative recessive epistasis (ratio is 9/16 to 7/17)
b. Indicate the possible genotype(s) that correspond to the phenotype of the F2
plants.
Purple = A-BYellow = A-bb; aaB-; aabb
c. Propose a biological model that explains color inheritance in these plants.
Precursor (yellow)
Intermediate (yellow)
Purple
A
B
If you have homozygous recessive in either gene, pathway is not complete
and color is yellow.
d. If crosses were set up between several different yellow F2 plants, what would you
expect the F3 plants to look like?
Yellow and purple because A-bb x aaB- or A-B- x A-B- gives both colors
5. In Drosophila the eye colors red, coral, wine, and white are controlled by multiple alleles
of a single gene (A). A red female is crossed with a white male and the progeny consist
of 55 red and 57 coral. Another red female is crossed with a coral male and the progeny
are 42 red and 49 wine.
a. What is the order of dominance for the four A alleles? Red > wine > coral > yellow
b. How many different eye color genotypes (for the A locus) can be present within a
population of flies in the wild? 10 (ArAr;; ArAwi ; ArAc; ArAwh; AwiAwi; AwiAc;
AwiAwh; AcAc; AcAwh; AwhAwh)
c. How many eye color alleles (for the A locus) can one fly possess? 2 max
Multiple choice section: (30 points total – 5 points per question)
Write your answer in the blank provided to the left
6. Identical twins look more similar to each than other than siblings do because identical twins
possess identical genes. However, genetically identical girl cats can have different coat color
patterns, whereas genetically identical male cats do not have different coat color patterns.
The most likely genetic reason for this is:
a. Penetrance
b. Epistasis
c. Multiple alleles
d. X-chromosome inactivation
e. Sex-influenced inheritance
7. Hairlessness in a particular breed of dogs is autosomal recessive to the presence of hair.
Suppose that you have a male dog with hair. How can you clearly determine whether this
dog is homozygous or heterozygous?
a. Mate the dog with a homozygous dominant dog
b. Mate the dog with its litter mates
c. Mate the dog with its mother
d. Mate the dog with a homozygous recessive dog
e. You can not determine the genotype since you do not know the male parent.
8.
Joe has Klinefelter syndrome (XXY) and is color blind. His mother and father have normal
color vision, but his maternal grandfather is colorblind. Colorblindness is inherited as an Xlinked, recessive trait. Assume that Bob’s abnormal sex chromosome number is due to
improper separation of either the homologous chromosomes or sister chromatids during
meiosis in one of his parents. In which parent and in which meiotic division did this aberrant
separation most likely occur?
a. Mom, meiosis I
b. Mom, meiosis II
c. Dad, meiosis I
d. Dad, meiosis II
e. Can not determine from the information given
9. For ABO blood type inheritance, the A allele is codominant to the B allele; the O allele is
recessive to both the A and B alleles. In a particular family, the father Joe’s blood type in
AB and the mother Ann’s blood type is O. The father and mother have four children with
the flowing blood types: AB, A, B, and O. One child is adopted and another is a child
from an earlier marriage of the mother (i.e. this child is the biological child of Ann, but
not the biological child of Joe). Which is the blood type of the adopted child?
a. A
b. B
c. AB
d. O
e. Can not determine from the information given
10. The Mendelian law that best describes why siblings do not look exactly the same is:
a. independent assortment.
b. multiple alleles.
c. equal segregation.
d. unit factors.
e. dominance and recessiveness.
11. A tall pure breeding plant was crossed with a dwarf pure breeding plant. The F1 plants
were all tall. Self crosses of the F2 gave a 68 tall and 32 dwarf plants. This data
resembles a 3:1 ratio, although not precisely. Therefore, you formulate the null
hypothesis that “The data recorded for this experiment do not differ significantly from the
3:1 ratio expected from a monohybrid cross” and do a chi2 analysis. You obtain a chi2
value of 2.61. Based on this statistical analysis, you:
a. reject your hypothesis.
b. accept your hypothesis.
c. use a lower critical chi square value.
d. use a higher critical chi square value.
e. Repeat the experiment because 100 progeny are not enough to be statistically
significant.
Table of chi2 critical values
df
1
2
3
4
5
0.90
0.02
0.21
0.58
1.06
1.61
0.50
0.46
1.39
2.37
3.36
4.35
Probability (p)
0.20
0.05
1.64
3.84
3.22
5.99
4.64
7.82
5.99
9.49
7.29
11.07
0.01
6.64
9.21
11.35
13.28
15.09
0.001
10.83
13.82
16.27
18.47
20.52