Biology 321 QUIZ#1
Winter 2011 Total points: 25
NAME________________________
1. (3 pts.) Genetic factors are thought to cause more than 50% of all cases of congenital hearing
loss (child is born deaf) in humans. Even though hundreds of genes are required for the
development and functioning of the inner ear, hereditary deafness is a single gene trait.
In one or two nicely crafted sentences explain the apparent contradiction in the second
statement. Student Answers:
Even though many genes are required for ear development and function, the mutation of just one
gene (component of development) can disrupt function. This is why hearing is considered a
single gene trait.
If there is a mutation in any one of the genes contributing to the development and functioning of
the inner ear, hereditary deafness will occur.
If many genes are necessary for inner ear development, then a defect in just one could easily
make it impossible for the ear to develop normally, if it controls a crucial protein.
NOTE: A single gene trait means that allelic variation in one of these genes can cause deafness.
It in no way implies that mutations in only one of the gene involved in the development and
functioning of the ear can cause deafness. Indeed mutations in many of these genes can result in
deafness
2. (2 pts.) Circle T or F for each statement. Answer false any part of the statement is false. If
there are two statements, the first statement is true and you are to decide if the second statement
is T or F.
FALSE Commercially valuable strains of strawberries can be 2n=14, 4n=28, 6n=42 or
8n=56. This information implies that these strains differ with respect to the number of different
chromosomes (double stranded DNA molecules per single genome copy.
TRUE The genome of the domestic dog (Canis familiaris) is summarized as 2n= 78.
Each product of meiosis I in the dog gonad would contain 39 chromosomes and 78 ds(doublestranded) DNA molecules and each product of meiosis II would contain 39 chromosomes and 39
ds DNA molecules.
3. (4pts. total) You self an F1 plant of genotype AaBbCc and select one F2 plant at random.
Assume all three genes are on different chromosomes. Show your work and circle your answer.
AaBbCc X AaBbCc
a. (2 pts.) What is the probability that this plant will be true-breeding for all three dominant
phenotypes? Truebreeding dominant = AABBCC = ¼ X ¼ X ¼ = 1/64
b. (1 pt.) What is the probability that a given F2 plant will be truebreeding for either the
dominant or recessive phenotype conferred by gene A?
either AA or aa = ¼ + ¼ = ½
c. (1 pt.) What is the probability that a given F2 plant will be truebreeding for all three genes?
extending calculation in b ½ X ½ X ½ = 1/8
hard way: figure out all possible genotypes and add their individual probabilities together:
AABBCC + aabbcc + AAbbCC etc. (8 different possibilities
1
4. (12 pts) You are exploring the inheritance of two traits in jimsonweed plants. The purple
smooth parent is from a true-breeding laboratory stock. The other parental plants were taken
directly from a field near Mt Baker. Different white parental plants were used in each cross
Trait
Flower color
Pod morphology
Alternative phenotypes
Purple or White
Spiny or Smooth
Progeny phenotypes: number in each class
C
R
O
S
S
Parental
phenotypes
White
Spiny
Purple
Smooth
White
Smooth
Purple
Spiny
1
White Smooth X
300
cW pSP pSM
100
300
100
c c
pSM pSM
c –
pSM pSM
cP cP
pSP pSM
200
cW cP
pSP pSM
200
200
200
W
P
c c p
SM
p
SM
White Spiny
P
P
W
cW cP pSP pSM
2
White Spiny X
W
c c
P
SP
p p
SM
Purple Smooth
cP cP
P
P
c c
pSM pSM
W
P
c c
pSM pSM
cP cP
pSP pSM
pSM pSM
a. Which trait flower color trait is dominant? WHITE
For part b, fill in the blank from the choices below. No explanation needed.
b. BOTH CROSSES (were) informative for determining dominance of this trait.
Cross 1 only Cross 2 only Both crosses
c. Which trait pod trait is dominant ? SPINY
For part d, fill in the blank from the choices below. No explanation needed.
d. CROSS 2 ONLY was (were) informative for determining dominance of this trait.
Cross 1 only Cross 2 only Both crosses
e. For each cross indicate the genotypes of the parents and progeny in the space underneath
the phenotype. Use these allele designations OR define your own alleles symbols below.
cP= purple
cW = white
pSP = spiny pod pSM = smooth pod
OPTIONAL: Use your own alleles symbols. Define them here:
2
5. (4 pts.) Examine the anaphase diagrams shown below which were taken from one your
assigned problems in Chapter 3. Each line represents a molecule of double-stranded DNA.
(Chromosomes will segregate as indicated.) The dotted line indicates where the cytoplasm will
be divided in cytokinesis. [HINT: If you are having trouble with these questions, think about
what the chromosome content would look like in metaphase.]
a. The diagram shown below is consistent with which of the scenarios listed below?
Choose all correct interpretations. Do not circle an option if any part of it is incorrect.
a. A 2n=4 cell undergoing mitosis
b. Meiosis I in a 2n=4 organism of genotype AaBb or AaBB
c. Meiosis I in a 2n=4 organism of genotype aaBB
d. Meiosis I in a 2n=2 organism of genotype aaBB
e. Meiosis II in a 2n=4 organism of genotype aaBB
f. Meiosis I in a 4n=4 organism


All B chromosomes
consist of two dsDNA
molecules 
b. The diagram shown below is consistent with which of the scenarios listed below?
Choose all correct interpretations. Do not circle an option if any part of it is incorrect
a. Mitosis in a 2n=4 cell of genotype AaBb
b. Mitosis in a 2n=8 cell of genotype AaBb
c. Mitosis in a 4n=4 cell
d. Meiosis I in a 2n=4 organism of genotype AaBb
e. Meiosis II in a 2n=8 organism
f. Meiosis II in a 4n=8 organism of genotype AAaaBBbb


3
Question
Score
(pts.)
1-3 ( 9 )
4 ( 12 )
5 ( 4)
Total 25 pts
4