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5-1
Biology 22
Practice Problems
Specific information for traits in the practice problems is provided in the tables on
pages 5-1 --- 5-3.
Chickens
Trait
Genotype
Phenotypic Effect
Relationship
Feather Color
C_
Colored feathers
(in absence of I allele)
White feathers
C>c
White feathers
(inhibits feather color from C)
I>i
cc
Color Inhibitor
I_
ii
Fruit Flies
Trait
Genotype
Phenotypic Effect
XYX-- or
XYY
Beige body (wild type)
XyeXye or
XyeY
Yellow body
Bristle Number
N_
Full Bristle Number (wild type)
(chromosome 2)
nn
Reduced Bristle Number
XFX-- or
XFY
Straight bristles (wild type)
XfXf or
XfY
Forked bristles
Eye Color
R_
Red eyes (wild type)
(chromosome 2)
rr
Cinnabar eyes
XWX-- or
XWY
Red eyes (wild type)
XwhXwh or
White eyes
Body Color
(X chromosome)
Bristle Shape
(X chromosome)
Eye Color
(X chromosome)
Relationship
Y > ye
N>n
F>f
R>r
W > wh
XwhY
Wing shape
V_
Long wings (wild type)
(chromosome 2)
vv
Vestigial wings
V>v
5-2
Specific information for traits in the practice problems is provided in the tables on
pages 5-1---5-3.
Humans
Trait
Genotype
Phenotypic Effect
ABO Blood Type
IAIA or IAi
Type A Blood
IBIB or IBi
Type B Blood
IAIB
Type AB Blood
ii
Type O Blood
XaXa or XaY
Angiokeratoma
(abnormal skin growths)
Angiokeratoma
XAX- or
Relationship
IA = IB > i
A>a
No disease
XAY
Earlobe attachment
E_
Free earlobes
ee
Attached earlobes
X FX f
Focal Dermal Hypoplasia (skin lesions)
Focal Dermal
Hypoplasia
X FY
Lethal (fetus dies in utero)
XfXf or
XfY
No disease
Hair Curling
wwo
Wooly hair
Hierarchy of
wk
Kinky hair
Dominance:
wc
Curly hair
wwo > wk >
wwa
Wavy hair
wc > wwa >
ws
Straight hair
ws
H_
Straight thumb
hh
Hitchhiker’s Thumb
(Last joint of thumb bends at 45o angle)
P_
Pigmented Iris
(Additional genes give specific color,
e.g. brown, hazel)
Hitchhiker’s Thumb
Iris Color
Mid-digital Hairs
Duchenne Muscular
Dystrophy
pp
Blue Iris (non-pigmented)
M_
Mid-digital Hairs
(Hairs on middle bone of fingers)
mm
Hairless mid-digits
XDX- or
X DY
No disease
XdXd or
Duchenne Muscular Dystrophy
E>e
F>f
H>h
P>p
M>m
D>d
XdY
Rh Factor
R_
Rh-positive blood
rr
Rh-negative blood
R>r
5-3
Specific information for traits in the practice problems is provided in the tables on
pages 5-1 --- 5-3.
Radishes
Trait
Genotype Phenotypic Effect
Relationship
Radish shape
LL
Long radish
Incomplete
L’L
Oval radish
Dominance
L’L’
Round radish
L + L’ = LL’
RR
Red radish
Incomplete
RR’
Purple radish
Dominance
R’R’
White radish
R + R’ = RR’
Radish color
Tomatoes
Trait
Genotype Phenotypic Effect
Fruit Color
R_
Red fruit
rr
Yellow fruit
T_
Tall
tt
Dwarf
M_
Uniformly green
mm
Mottled (patches of yellow)
O_
Round
oo
Oblate
Plant size
Leaf Coloration
Fruit Shape
Relationship
R>r
T>t
M>m
O>o
5-4
Specific information for traits in the practice problems is provided in the tables on
pages 5-1 --- 5-3.
A. Frank has attached earlobes. His wife Flora has free earlobes but Flora’s
father has attached earlobes.
a. What is the probability that Frank and Flora will have a child with free
earlobes?
b. Out of 3 children born to Frank and Flora, what is the probability that at
least one child will have attached earlobes?
c. Out of 4 children born to Frank and Flora, what is the probability that 3
children will have free earlobes?
B. Thomas has mid-digital hairs. His wife Theresa also has mid-digital hairs.
Their first child, Theodore, has hairless mid-digits.
a. What is the probability that Thomas and Theresa’s second child will have
mid-digital hairs?
b. What is the probability that Thomas and Theresa’s third child will have
hairless mid-digits?
c. Out of 5 children born to Thomas and Theresa, what is the probability that
at least 1 will have mid-digital hairs?
C. Paul has light blue non-pigmented irises. His wife Pamela also has nonpigmented irises.
a. What is the probability that Paul and Pamela will have a child with
pigmented irises?
b. What is the probability that Paul and Pamela will have a child with nonpigmented irises?
D. Ernest has Type AB, Rh-positive blood. His wife Emily has Type A, Rhpositive blood. Ernest’s mother has Type B, Rh-negative blood. Emily’s father
has Type O, Rh-negative blood. What is the probability that Ernest and Emily
will have a child with
a. Type AB, Rh-negative blood?
b. Type B, Rh-positive blood?
c. Type A, Rh-negative blood?
d. Type B, Rh-negative blood?
e. Type A, Rh-positive blood?
f. Type AB, Rh-positive blood?
g. Type O, Rh-negative blood?
5-5
Specific information for traits in the practice problems is provided in the tables on
pages 5-1 --- 5-3.
E. Jeremy has attached earlobes and pigmented irises. His wife Jenny has free
earlobes and light blue non-pigmented irises. Jeremy’s father has nonpigmented irises. Jenny’s mother has attached earlobes.
a. What is the probability that Jeremy and Jenny will have a child with free
earlobes and pigmented irises?
b. What is the probability that Jeremy and Jenny will have a child with
attached earlobes and non-pigmented irises or free earlobes and nonpigmented irises?
c. Out of 4 children born to Jeremy and Jenny, what is the probability that 2
will have attached earlobes and pigmented irises?
F. Mark has straight hair. His wife Marilyn has curly hair. Their son Matthew has
straight hair. For Mark and Marilyn, what is the probability that
a. Their second child will have curly hair?
b. Out of 3 children, two will have straight hair?
c. Out of 4 children, at least one will have curly hair?
G. Mr. X has angiokeratoma. He marries Ms. Y who does not have
angiokeratoma but whose father has the disease. What are the expected
percentages and phenotypes (including gender) for children of Mr. X and Ms.
Y?
H. What are the percentages and phenotypes of offspring for the following fruit fly
crosses involving body color genes?
a. Yellow-bodied female X Beige-bodied male?
b. True-breeding Beige-bodied female X Yellow-bodied male?
c. Beige-bodied female (from Yellow-bodied father) X Yellow-bodied male?
I.
A plant with round, red radishes is crossed to a plant with long, white
radishes. The F1 plants were crossed to plants with round, purple radishes. In
the resulting F2 generation, what is the fraction of plants that will have
a. Oval, purple radishes?
b. Oval, white radishes?
c. Long, red radishes?
d. Round, red radishes?
e. Long, purple radishes?
f. Round, white radishes?
g. Oval, red radishes?
h. Round, purple radishes?
i. Long, white radishes?
5-6
Specific information for traits in the practice problems is provided in the tables on
pages 5-1 --- 5-3.
J. A true-breeding red, dwarf tomato plant is crossed to a true-breeding yellow,
tall tomato plant to produce an F1 generation. F1 plants are crossed to each
other to produce an F2 generation.
a. What are the genotypic and phenotypic ratios for the offspring in the F1
generation?
b. What are the genotypic and phenotypic ratios for the offspring in the F2
generation?
K. A rooster with white feathers is mated to a hen with white feathers. Both the
rooster and hen are heterozygous for both the C and I genes governing
feather color. In the next generation, what is the ratio of offspring with colored
feathers to offspring with white feathers?
L. Nancy has Focal Dermal Hypoplasia. Her husband Norm does not have the
disease. Considering only children born alive to Nancy and Norm, what
fraction will be
a. Females with Focal Dermal Hypoplasia?
b. Males without Focal Dermal Hypoplasia?
c. Females without Focal Dermal Hypoplasia?
M. In fruit flies, three genes on the first chromosome (the X chromosome for sex
determination) affect body color, eye color and bristle shape. The recessive traits are
yellow body (allele ye), white eyes (allele wh) and forked bristles (allele f). The
corresponding dominant traits are beige body (allele Y), red eyes (allele W) and long
bristles (allele F). A female true breeding for yellow body, red eyes and long bristles
was mated to a male true breeding for beige body, white eyes and forked bristles.
The F1 females, with beige bodies, red eyes and long bristles, were mated to males
with yellow bodies, white eyes and forked bristles. The resulting F2 offspring are
listed below.
Body color
Eye color
Bristle shape
Number of offspring
yellow
red
long
376
beige
white
forked
388
yellow
white
forked
6
beige
red
long
8
beige
red
forked
41
yellow
white
long
45
yellow
red
forked
66
beige
white
long
70
a.
b.
Draw a genetic map that shows the distances between these genes.
What is the degree of interference for these genes?
5-7
N. In tomatoes, three genes on the first chromosome affect leaf coloration, fruit shape
and plant height. The recessive traits are mottled leaves (allele m), oblate fruits
(allele o) and dwarf height (allele t). The corresponding dominant traits are green
leaves (allele M), round fruits (allele O) and tall height (allele T). A plant that is true
breeding for mottled leaves, round fruits and dwarf height is crossed to a plant that is
true breeding for green leaves, oblate fruits and tall height. The F1 plants, with green
leaves, round fruits and tall heights are mated to plants that are true breeding for
mottled leaves, oblate fruits and dwarf height. The resulting F2 offspring are listed
below.
Leaf Coloration
mottled
green
Fruit Shape
round
oblate
Plant Height
dwarf
tall
Number of Offspring
320
312
mottled
green
green
mottled
green
mottled
round
oblate
round
oblate
round
oblate
tall
dwarf
tall
dwarf
dwarf
tall
10
12
96
102
79
69
a. Draw a genetic map that shows the distances between these genes.
b. What is the degree of interference for these genes?
O. In fruit flies, three genes on the second chromosome (an autosome) affect eye color,
bristle number and wing shape. The recessive traits are cinnabar eyes (allele r),
reduced bristle number (allele n) and vestigial wings (allele V). The corresponding
dominant traits are red eyes (allele R), full bristle number (allele N) and long wings
(allele V). A female true breeding for cinnabar eyes, reduced bristle number and
vestigial wings was mated to a male true breeding for red eyes, full bristle number
and long wings. F1 females, with red eyes, full bristle number and long wings, were
mated to males with cinnabar eyes, reduced bristle number and vestigial wings. The
resulting F2 offspring are listed below.
Eye color
Bristle Number
Wing shape
Number of offspring
Cinnabar
Reduced
Vestigial
810
Red
Full
Long
818
Cinnabar
Reduced
Long
113
Red
Full
Vestigial
119
Cinnabar
Full
Vestigial
69
Red
Reduced
Long
63
Cinnabar
Full
Long
5
Red
Reduced
Vestigial
3
a.
b.
Draw a genetic map that shows the distances between these genes.
What is the degree of interference for these genes?
5-8
P. Neurospora crassa produces ordered tetrads. The numbers and types of
tetrads that result from three crosses are shown below. Spores are listed in
pairs for simplicity. Draw a genetic map that represents the distances
between these three genes (A, B and C) and also shows the distance
between each gene and its centromere.
Cross 1: A B x a b
A B
A B
a b
a b
292
A
A
a
a
b
b
B
B
22
A
A
a
a
b
B
b
B
6
A
a
A
a
b
b
B
B
38
A
a
A
a
B
b
B
b
16
A
a
A
a
b
B
b
B
14
A
a
A
a
B
b
b
B
12
Cross 2: A C x a c
A C
A C
a c
a c
233
A
A
a
a
c
c
C
C
19
A
A
a
a
c
C
c
C
68
A
a
A
a
c
c
C
C
38
A
a
A
a
C
c
C
c
12
A
a
A
a
c
C
c
C
18
A
a
A
a
C
c
c
C
14
Cross 3: B C x b c
B C
B C
b c
b c
288
B
B
b
b
c
c
C
C
0
B
B
b
b
64
c
C
c
C
B
b
B
b
c
c
C
C
0
B C
b c
B C
b c
48
B
b
B
b
0
c
C
c
C
B C
b c
B c
b C
0
5-9
Q. Neurospora crassa produces ordered tetrads. The numbers and types of
tetrads that result from three crosses are shown below. Spores are listed in
pairs for simplicity. Draw a genetic map that represents the distances
between these three genes (D, E and F) and also shows the distance
between each gene and its centromere.
Cross 1: D e
D
D
d
d
E
E
e
e
14
D
D
d
d
e
e
E
E
264
D
D
d
d
e
E
e
E
2
D
d
D
d
e
e
E
E
90
x d E
D
d
D
d
E
e
E
e
12
D e
d E
D e
d E
10
D
d
D
d
E
e
e
E
8
Cross 2: E F x e f
E F
E F
e f
e f
E
E
e
e
f
f
F
F
155
149
E
E
e
e
f
F
f
F
64
E
e
E
e
f
f
F
F
E F
e f
E F
e f
E f
e F
E f
e F
8
14
0
E
e
E
e
F
f
f
F
10
Cross 3: D f x d F
D F
D F
d f
d f
D
D
d
d
f
f
F
F
102
104
D
D
d
d
74
f
F
f
F
D
d
D
d
f
f
F
F
98
D
d
D
d
F
f
F
f
10
D
d
D
d
8
f
F
f
F
D
d
D
d
4
F
f
f
F
5-10
R. Two Hfr strains carrying the markers thr+ leu+ azis lac+ gal+ were individually
conjugated with an F- strain with the genotype thr- leu- azir lac- gal-. Samples
were removed at various times and the incorporation of markers into the
recipient strains by recombination was determined, as shown below.
Time
(min)
0
Recombinants with
markers
form Hfr strain 1
None detected
Time
(min)
0
Recombinants with
markers
from Hfr strain 2
None detected
4.0
azis
5.0
thr+
7.0
azis leu+
9.0
thr+ leu+
11.0
azis leu+ thr+
12.0
thr+ leu+ azis
18.0
azis leu+ thr+ gal+
20.0
thr+ leu+ azis lac+
29.0
azis leu+ thr+ gal+ lac+
31.0
thr+ leu+ azis lac+ gal+
Draw a map showing the locations of these genes on the E. coli chromosome.
S. An Hfr strain that is cysH+ metB- argA+ strs is conjugated with an F- strain
that is cysH- metB+ argA- strr. Interrupted mating studies show that cysH+
enters last. Recombinants that are cysH+ strr are selected and then tested for
the presence of metB+ and argA+. The following numbers of bacteria are
found for each of the genotypes listed below. Draw a map that shows the
gene order and the distances between the genes in map units.
Class
+
Number of exconjugants
+
-
cysH metB argA
78
cysH+ metB+ argA+
53
+
-
-
cysH metB argA
2
cysH+ metB- argA+
367
T. DNA is isolated from E. coli strain V (lys- pro- pens) and used to transform
strain W (lys+ pro+ pens). Transformants are selected on minimal medium +
penicillin to kill lys+ pro+ cells and survivors are plated on complete medium.
The classes and numbers of cells obtained are listed below. Draw a map that
shows the distance between the lys and pro genes based on recombination
frequency.
Class
Number of Transformants
+
-
lys pro
19
lys- pro+
26
-
-
lys pro
205
5-11
U. Transducing phages that infected a gal+ trp+ his+ cell were used to infect a
gal- trp- his- cell. Transductants receiving the gal+ marker were tested for the
presence of trp+ and his+. The classes and numbers of transductants for
each class are shown below. Determine the gene order and the
cotransduction frequencies of gal+ with trp+ and gal+ with his+.
Class
Number of Transductants
gal+ trp+ his+
22
gal+ trp+ his-
3
gal+ trp- his+
78
gal+ trp- his-
397
V. The tables below show the offspring from three crosses with bacteriophage of
alternate genotypes. Determine the order and genetic distances for genes A,
B and C.
A- B+
A- B-
A+ B-
A+ B+
457
42
453
48
A- C+
A- C-
A+ C-
A+ C+
419
83
411
87
B- C+
B- C-
B+ C-
B+ C+
376
124
364
136
Cross
A- B+ X A + B-
Cross
A- C+ X A+C -
Cross
B- C+ X B+C -
W. In a human population exhibiting Hardy-Weinberg Equilibrium for the eye
pigmentation gene, 81% of the people have blue (non-pigmented) irises. For this
population
a.
b.
c.
d.
What is the frequency of the allele for blue irises?
What is the frequency of the allele for pigmented irises?
What is the frequency of people who are homozygous for pigmented irises?
What is the frequency of people who are heterozygous for pigmented irises?
5-12
X. Human Population A exhibits Hardy-Weinberg Equilibrium for the Duchenne
Muscular Dystrophy gene. In this population, 3% of the males have the
disease. For Population A
a. What is the frequency of females with Duchenne Muscular Dystrophy?
b. What is the frequency of females who are carriers of the Duchenne
Muscular Dystrophy allele?
c. What is the frequency of females who are homozygous for the nondisease allele (DD)?
Y. Human Population B exhibits Hardy-Weinberg Equilibrium for the Duchenne
Muscular Dystrophy gene. In Population B, 9% of the males have the
disease. A representative group of 1000 individuals from Population B
migrates to a small isolated island to join 1000 representative individuals from
Population A. (Assume equal number of males and females in both
populations and that both populations are in Hardy-Weinberg Equilibrium at
all times.) In the new mixed population immediately after immigration, what is
the
a. frequency of males with Duchenne Muscular Dystrophy?
b. frequency of females with Duchenne Muscular Dystrophy?
Z. In a human population that does not exhibit Hardy-Weinberg Equilibrium for
Duchenne Muscular Dystrophy, the frequency of the disease allele (d) is 0.3
in males and 0.2 in females. Considering random mating to produce the next
generation
a. What percentage of male offspring will have Duchenne Muscular
Dystrophy?
b. What percentage of female offspring will have Duchenne Muscular
Dystrophy?