Download Patterns of Inheritance Worksheet_Key

Patterns of Inheritance Worksheet
Name: ________________________
1. Complete the following monohybrid cross. The P generation is true breeding. Cross a plant that
produces yellow seeds with a plant that produces green seeds. Yellow is dominant. Use Y for yellow, y
for green.
P generation phenotype:
genotype:
yellow seeds
YY
green seeds
yy
gametes produced:
all Y
all y
F1 generation phenotype:
genotype:
yellow seeds
Yy
gametes produced:
1/2 Y, 1/2 y
F2 generation (cross F1 with F1)
Y
y
Y
YY
Yy
y
Yy
yy
Possible phenotypes: Yellow, Green
Ratios:
3/4,
1/4
Possible genotypes: YY, Yy, yy
Ratios:
1/4, 2/4, 1/4
______________________________________________________________________________
2. Complete the following monohybrid cross. The P generation is true breeding. Cross a tall plant with
a short plant. Tall is dominant. Use T for tall, t for short
P generation phenotype:
genotype:
tall
TT
short
tt
gametes produced:
all T
all t
F1 generation phenotype:
genotype:
Tall
Tt
gametes produced:
1/2 T, 1/2 t
F2 generation (cross F1 with F1)
T
t
T
TT
Tt
t
Tt
tt
Possible phenotypes: Tall, Short
Ratios:
3/4, 1/4
Possible genotypes: TT, Tt, tt
Ratios:
1/4, 2/4, 1/4
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3. Complete the following dihybrid cross for seed pod traits. Assume the genes are linked. Green is
dominant. Use G for green, g for yellow. Inflated is dominant. Use I for inflated, i for constricted.
P generation phenotype:
genotype:
yellow constricted pod
gi
gi
green inflated pod
GI
GI
gametes produced:
all gi
all GI
F1 generation phenotype:
genotype:
green inflated pod
GI
gi
gametes produced:
1/2 GI, 1/2 gi
F2 generation (cross F1 with F1)
GI
gi
GI
GGII
GgIi
gi
GgIi
ggii
Possible phenotypes: green inflated pod, yellow constricted pod
Ratios:
3/4,
1/4
Possible genotypes: GGII, GgIi, ggii
Ratios:
1/4, 2/4, 1/4
__________________________________________________________________________________
4. Complete the following dihybrid cross for seed pod traits. Assume the genes are NOT linked.
Green is dominant. Use G for green, g for yellow. Inflated is dominant. Use I for inflated, i for
constricted.
P generation phenotype:
yellow constricted pod
green inflated pod
genotype:
gi
GI
gametes produced:
all gi
all GI
F1 generation phenotype:
genotype:
green inflated pod
GgIi
gametes produced:
GI, Gi, gI, gi
F2 generation (cross F1 with F1)
GI
Gi
gI
gi
GI
GGII
GGIi
GgII
GgIi
Gi
GGIi
GGii
GgIi
Ggii
gI
GgII
GgIi
ggII
ggIi
gi
GgIi
Ggii
ggIi
ggii
Possible phenotypes: green inflated, green constricted, yellow inflated, yellow constricted
Ratios:
9/16
3/16
3/16
1/16
Possible genotypes: GGII, GGIi, GgII, GgIi, GGii, Ggii, ggII, ggIi, ggii
Ratios:
1/16, 2/16, 2/16, 4/16, 1/16, 2/16, 1/16, 2/16, 1/16
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5. For the following results of a dihybrid F2 cross, determine whether of not the genes are linked.
a) 1 white short plant, 9 purple tall plants, 3 white tall plants and 3 purple short plants.
Genes are not linked. Purple is dominant, white is recessive. Tall is dominant, short is recessive (from
lecture notes & book). Ratio is 9:3:3:1, with dominant phenotype for both traits at 9 and recessive
phenotype for both traits at one. This matches the phenotype reached in a dihybrid cross when the genes
are not linked.
b) 12 purple tall, 4 white short
Genes are linked (in this example). This ratio shows a 3:1 phenotypic ratio (divide each number by 4),
with 3 dominant phenotypes and 1 recessive phenotype.
6. You have a purple flowered plant, but do not know whether or not it is true breeding or not. How
could you determine whether it is homozygous or heterozygous for that trait? Show all your work.
Perform a test cross and analyze results. Cross between unknown genotype of purple flowered plant,
with a recessive (and true breeding) white flowered plant
Cross:
purple flower
white flower
P_
pp
Results:
Possibility one: Purple flower is homozygous
P
P
p
Pp
Pp
p
Pp
Pp
All offspring will have purple flowers
Possibility two: Purple flower is heterozygous
P
p
p
Pp
pp
p
Pp
pp
1/2 of offspring purple, 1/2 of offspring white
Note: it is possible, under the rules of probability, never to get white offspring in the 2nd possibility.
The test cross is only really definitive if you do get white offspring, or if you do a very large number of
crosses and never get white offspring.
7. You are a genetics counselor at a hospital. A couple, both of whom are carriers of cystic fibrosis, a
recessive disease, want to know what the chances are that their offspring would have cystic fibrosis.
What would you tell them? Show all your work.
C = normal, c = cystic fibrosis
Both parents are carriers, so both heterozygous (Cc)
C
c
C
CC
Cc
c
Cc
cc
They have a 1/4 chance of producing a child with cystic fibrosis, every time they have a child.
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8. The same couple decide to use a healthy sperm donor with the mother’s egg. What are their chances
that their offspring would have cystic fibrosis? What about being a carrier?
C = normal, c = cystic fibrosis
Mother is carrier, so is heterozygous (Cc)
Sperm donor is normal, so homozygous dominant (CC)
C
C
C
CC
CC
c
Cc
Cc
They will not produce a child with cystic fibrosis, however, they do have a 50% possibility of producing
a child who is a carrier of cystic fibrosis, every time they have a child.
9. A human female "carrier" who is heterozygous for the recessive, sex-linked trait causing red-green
color blindness, marries a normal male. What proportion of their female children will have red-green
color blindness? What proportion of their male children will have red-green color blindness? Show all
your work.
C = normal, c = red-green color blind
Female = XCXc
Male = XCY
C
X
Xc
XC
XC XC
XCXc
Y
XC Y
XcY
Females = 100% normal (50% carriers)
Males = 50% normal, 50% red-green color blind
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