Name _________________________
Biology 201 (Genetics)
Exam #1

Read the question carefully before answering. Think before you write. Be concise.

You will have up to one hour to take this exam. After that, you MUST stop no matter
where you are in the exam.

If I can not read your handwriting, I will count the question wrong.

Use clear gene symbols (i.e. Aa is easier to distinguish that Oo).

Sign the honor pledge if applicable.

Good luck!
I pledge that I have neither given nor received unauthorized assistance during the completion
of this work.
Signature: __________________________________________________________
Problems section:
1. Below is a pedigree of a rare human hereditary trait controlled by one gene. The boxes
represent males and circles represent females. Shading symbolizes the abnormal phenotype.
a. is the inheritance pattern X-linked or autosomal? X-linked (recessive) was the best answer
since mostly males had the abnormal phenotype. Affected females gave the trait to all
sons, but no daughters. I did accept autosomal since statistically one might argue that not
enough individuals were examined to conclusively prove sex-linked.
b. dominant or recessive? recessive
c. Give the genotype of each individual in the pedigree. If more than one genotypic
possibility exists, present all possible alternatives. see below for x-linked in red or if you
told me autosomal in green)
d. If the women marked with an * marries an unaffected male, what is the probability that
they would have an affected child?
For sex-linked = 1/2 *1/4 = 1/8
For autosomal = 2/3*0 (remember a allele is rare)*1/4 = 0
XAY
XAXA
XAY
a
A
XaXa
a
XY X X
XAXa
XAXa
a
Aa
aa
Aa
XAY
XAX- XAY- XAX- XAX-
Aa
Aa
a
XY X X
Aa
AA
A
XaY
aa
aa
A-
Aa
Aa
A-
A-
A-
aa
Consider a diploid organism where the hair color gene A is on one autosome, the eye color gene
B is on another autosome, and sex determination is via an XX/XY mode. A male individual is
heterozygous for hair color and eye color.
e. Draw a cell of a male showing the chromatin before DNA duplication.
A
B
b
a
X
Y
f. Draw a cell of a male showing the chromosomes during metaphase of mitosis.
Label the homologous chromosomes and sister chromatids. In one sentence, tell what is
the difference between the homologous chromosomes and sister chromatids.
Homo. Chrom. =
A and a
B and b
X and Y
Y
X
A
b
a
B
Y
X
A
b
a
B
Sister
chromatids
Homologous chromosomes have the same genes but the alleles (flavors) of the genes may
be different, while sister chromatids are exact duplicates of the chromosome.
g. How many cells are produced from the mitosis? _2_ How many chromosomes are in
each cell? _6_
h. Draw one possible cell of a male showing the chromosomes during metaphase I of
meiosis.
X
A
B
B
Y
a
b
i. How many cells are produced from the meiosis? __4__ How many chromosomes are in
each cell? __3__
j. What is the genetic function of meiosis?
To generate haploid gametes for fertilization. Meiosis generates genetic variability through
crossover and alignment of the homologous chromosomes during metaphase I.
2. You have two pure breeding strains of Drosophila:
Strain #1 has brown eyes and normal length wings.
Strain #2 has red eyes and no wings.
You cross strain # 1 with strain #2 and obtain F1 flies that are red eyes and have shortened
wings.
You mate members of the F1 generation and obtain F2 individuals as follows:
# of flies phenotype
30
normal wings, red eyes
10
normal wings, brown eyes
60
shortened wings, red eyes
20
shortened wings, brown eyes
30
no wings, red eyes
10
no wings, brown eyes
a. Based on these data, what is the inheritance pattern of wing length (be sure to indicate the
type of dominance)? Incomplete dominance because intermediate phenotype in the F1
progeny and 1:2:1 in F1XF1 progeny. Codominance is not correct because there is no
evidence of both traits being expressed.
b. Based on these data, what is the inheritance pattern of eye color (be sure to indicate the
type of dominance)? Classical, simple dominance where red eye is dominant to brown
eye.
3. You and your pal Gene are bird breeders. You cross a pure breeding green-feathered bird
with a pure breeding white-feathered bird and you get F1 green-feathered birds.
You mate the F1 birds with each other and are surprised to get:
8 green-feathered
4 yellow-feathered
3 blue-feathered
1 white-feathered
You think that this is a case of multiple alleles, since you see more that two types of feather
colors. You pal Gene thinks that this is a case of two genes affecting one character.
Which hypothesis is right? Two genes controlling one character (Gene).
Clearly explain WHY one hypothesis is correct and the other is wrong? The fact that the F2
progeny are in 16th suggests two genes controlling one character. Green feathers would be A-B-, yellow would
be A-bb, blue would be aaB-, and white would be aabb. Thus the parental cross was AABB x aabb  AaBb
F1. F1 x F1 would give you the F2 progeny ratios seen. Additionally, this can NOT be multiple alleles
because you begin with pure breeding birds. Even if there were multiple alleles, there would only be two alleles
in this problem because initial green bird would be homozygous for one allele, and initial white bird would be
homozygous for the other. Since the F1 birds were mated with each other, you still only have two total alleles
that can contribute to the F2 progeny.
Epistasis is incorrect because there would be less than three classes in the F2 if one gene pair masked another
gene pair. Incomplete dominance also is incorrect because you can still not explain the white bird ratios.
4. In your garden you have some plants that have solid leaves and others have striped leaves.
You conduct a series of crosses and obtain the results given in the table.
Cross
Progeny
Solid
Striped
____________________________________________________________________________
(a)
(b)
(c)
(d)
(e)
solid ð
solid ð
striped
solid ð
solid ð
striped
solid
ð striped
solid
striped
___Aa
___AA
___aa
___Aa
___AA
X
X
X
X
X
aa___
A-___
aa___
Aa___
aa___
55
36
0
92
44
60
0
65
30
0
a. Which trait is dominant and which cross told you this?
Solid – cross d or e
b. Define gene symbols (using A and a) and give the possible genotypes of the parents of
each cross. Write your final answer in the blank next to the cross.
See above
Multiple choice section: (15 points total – 3 per question)
1.
If a typical somatic cell has 32 chromosomes, how many chromosomes are expected in
each gamete of that organism?
a. 32
b. 64
c. 16
d. 0
e. 46
2.
An allele is
a. one of the bases in DNA.
b. an alternate form of a gene.
c. one of multiple different genes that interact to affect one character.
d. present only in males and is responsible for sex determination.
e. one of the genes that is on the sister chromatid
3.
What types of phenotypic ratios are likely to occur in crosses of heterozygotes when
dealing with a single gene pair?
a. 9:3:3:1, 1:2:1
b. 9:3:3:1
c. 3:1, 1:1, 1:2:1
d. 3:1
e. 3:1, 1:2:1
4.
In humans, the genetic basis for determining the sex "male" is accomplished by the
presence of
a. a portion of the Y chromosome.
b. one X chromosome.
c. a balance between the number of X chromosomes and the number of sets of autosomes
d. high levels of testosterone.
e. the entire Y chromosome
6. Mendel’s law of independent assortment can be applied to:
a. Mitosis
b. Meiosis I
c. Both mitosis and meiosis
d. Meiosis II
e. Both A and D
7. You study fur length in cats. Short fur is dominant to long fur. You have a short-haired cat.
How would you determine whether it is homozygous or heterozygous?
a. Mate the cat with a homozygous dominant
b. Mate the cat with a homozygous recessive
c. Mate the cat with its litter mates
d. You can not determine the genotype since you do not know the parents.
e. None of the above