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Genetics contest 1 Prof. Sabrina Pricl A.Y. 2020-2021
Genetics contest 1
Prof. Sabrina Pricl A.Y. 2020-2021
Hornless (H) in cattle is dominant over horned (h). A homozygous hornless bull is mated with a homozygous horned cow. What will be the genotypes and phenotypes of the offspring? Which percentage each? Explain.
Question 1
2Elements of Chemical and Molecular Biology – Genetics contest 1
H H
h
h
Hhhornless
P1
P2
Hh 100%Genotype ratio – (1 single G) Phenotype ratio: - (100% hornless)
hornless
Hhhornless
Hhhornless
Hhhornless
Brown eyes in humans (B) are dominant to blue eyes (b). A brown-eyed man, whose mother was blue-eyed, marries a brown-eyed woman whose father has blue eyes. What is the probability that this couple will have a blue-eyed child? Explain.
Question 2
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B b
B
b
BBbrown
Bbbrown
P1
P2BB brown 25%50%
bbblue
Bbbrown
Genotype ratio 1:2:1 Phenotype ratio: 3:1
Bbbb
brownblue 25%
The probability of having a blue-eyed child is 25%
Elements of Chemical and Molecular Biology – Genetics contest 1
The color of flowers in snapdragons shows incomplete dominance. Red (RR) and white snapdragons (WW) are homozygous and pink (RW) is heterozygous.a. If a red snapdragon is crossed with a white snapdragon, what are the genotypes and the phenotypes of the offspring? And the percentage of each? Explain.
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Question 3 a
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R R
W
W
RWpink
P1
P2
RW 100%Genotype ratio – (1 single G) Phenotype ratio: - (100% hornless)
pink
RWpink
RWpink
RWpink
Elements of Chemical and Molecular Biology – Genetics contest 1
The color of flowers in snapdragons shows incomplete dominance. Red (RR) and white snapdragons (WW) are homozygous and pink (RW) is heterozygous.b. A pink flower is crossed with a red flower. What are the genotypes and the phenotypes of the offspring? And the percentage of each? Explain.
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Question 3 b
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R W
R
R
RRred
P1
P2
RW 50%
Genotype ratio: 1:1 Phenotype ratio: 1:1
pink
RWpink
RRred
RWpink
RR red 50%
Elements of Chemical and Molecular Biology – Genetics contest 1
The color of flowers in snapdragons shows incomplete dominance. Red (RR) and white snapdragons (WW) are homozygous and pink (RW) is heterozygous.c. What crossing is required to obtain 50% white snapdragons? What are the genotypes and the phenotypes of the offspring resulting from this crossing? And the percentage of each? Explain.Answer: RW x WW
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Question 3 c
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R W
W
W
RWpink
P1
P2
RW 50%
Genotype ratio: 1:1 Phenotype ratio: 1:1
pinkWWwhite
RWpink
WWwhite
WW 50%white
Elements of Chemical and Molecular Biology – Genetics contest 1
Sickle cell anemia is a pathologic condition that shows codominance. The genotype for normal blood cells is NN. Sickle cell trait is the heterozygous condition (NS) and blood contains both normal and sickle cells. Sickle cell disease is the homozygous condition (SS) and all blood cells are sickle-shaped and has life-long medical implication.
A man with sickle cell trait has a child with a woman with sickle cell trait. What are the genotypes and phenotypes of the offspring? And the percentage of each? Explain.
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N S
N
S
NNnormal
NSnormalcarrier
P1
P2
SSaffected
NSnormalcarrier
Genotype ratio 1:2:1 Phenotype ratio: 1:2:1
Question 4
NNNSSS
normalnormal, carrier
affected
25%
50%25%
Elements of Chemical and Molecular Biology – Genetics contest 1
You are a sheep breeder and received a brown male sheep as a present for your birthday. You know that brown fur color (B) for sheeps is dominant to white fur color (b). Yet, in order to breed your new sheep with your herd you need to know the sheep genotype. What will you do? Perform the experiment, report the results and explain.
You do a Test cross usinga True Breeding Strain (TBS) sheep
You choose a sheep with G(b,b)You cross your new sheep with unknownG with the G(b,b) sheepIf you get all brown sheeps the G ofyou new sheep must be (B,B)
If you get 50% brown sheeps and 50%white sheeps then the G of your newsheep must be (B,b)
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Question 5
Elements of Chemical and Molecular Biology – Genetics contest 1
A man with type O blood marries a woman with heterozygous A blood type.a. What are the possible genotypes and phenotypes of
the offspring?b. b. What are the probability of each genotype and
each phenotype?
Question 6 a/b
O O
A
O
AOA
AOA
P1
P2
OOO
OOO
AO 50%
Genotype ratio: 1:1 Phenotype ratio: 1:1
A
OO 50%OO
Elements of Chemical and Molecular Biology – Genetics contest 1
If a man with blood type AB marries a woman with type blood B, can they have a child with blood type O? (quick answer)NO – father G(A,B)
mother G either (BO) or (BB)neither a cross AB x BB or a cross AB x BO would give an offspring with G(OO)
Question 6 c
Elements of Chemical and Molecular Biology – Genetics contest 1
In humans a gene for normal blood clotting (N) is dominant to the gene for abnormal blood clotting (n) (the related inherited disease is called hemophilia, resulting in spontaneous bleeding as well as hard-to-stop bleeding following injuries or surgery). The gene for blood clotting is on the X chromosome. A hemophilia carrier woman (suggestion: heterozygous) marries a man with hemophilia. What is the probability for the couple having:a. a normal, non-carrier daughter?b. a normal sonc. a hemophilic son
This couple (father G(XnY) and mother G(XNXn))has:a. 0% probability to have a normal, non-carrier daughterb. 25% probability to have a normal sonc. 25% probability to have a hemophilic son
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XN Xn
Xn
Y
XNXnf,normal,
carrier
XnXnf,hemophilic
P1
P2
XnYm,hemophilic
XNYm,normal
Question 7 a-c
Elements of Chemical and Molecular Biology – Genetics contest 1
Now suppose that a normal woman marries a man with hemophilia.
What is the probability for this couple having:
d. a hemophilic son?
e. a hemophilic daughter?
This couple (father G(XnY) and mother G(XNXN))
has:
d. 0% probability to have a hemophilic son
e. 0% probability to have a normal son
Remember: it is an X-linked recessive disease. If the mother is normal, you will have
50% probability to have a normal, carrier daughter and 50% to have normal sons
(try Punnett squares to convince yourself)
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Question 7 d/e
Elements of Chemical and Molecular Biology – Genetics contest 1
Question 8 – dihybrid crossesIn humans, tall (T) is dominant to short (t) and brown
eyes (B) is dominant on blue eyes (b). If a tall brown-
eyed man marries a tall brown-eyed woman, what is
the probability for the couple to have tall blue-eyed
offspring?
Your cross is TtBb x TtBb
Look for tall and blue eyes and remember:
- to be blue-eyed (recessive) genotype MUST be…
(bb)
- to be tall (dominant) genotype must be…
either (TT) or (Tt)
You than have TTbb (1/16) and Ttbb (2/16), with total
probability 3/16
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TB tBTb tbP1
P2
TB
Tb
tB
tb
TTBB TTBb TtBB TtBb
TTBb TTbb TtBb Ttbb
TtBB TtBb ttBB ttBb
TtBb Ttbb ttBb ttbb
Elements of Chemical and Molecular Biology – Genetics contest 1
