Download Key for Incomplete Dominance/Codominance Review

Name____________________________________Date________________Period____
Review on Incomplete Dominance/ Codominance
and Multiple Alleles
1. In snapdragon flowers, the red (CR) and white (CW) flower color alleles
exhibit incomplete dominance. Flowers with the genotype CRCW are pink.
Fill in the Punnett square below to determine the probabilities of different
offspring in a cross of two pink snapdragon flowers (CRCW x CRCW).
Pollen
Egg
CR
CW
CR
C RC R
C RC W
CW
C RC W
CWCW
Offspring Phenotypes: Red, Pink, White
Phenotype Ratio: 1:2:1
Probability of red flowered offspring 25%
Probability of pink flowered offspring 50%
Probability of white flowered offspring 25%
2. Circle all the traits below that exhibit incomplete dominance or
codominance.
3. Explain how you can determine which traits above show incomplete
dominance or codominance.
Traits for which the heterozygous individuals look different from either
type of homozygous individuals.
4. In cattle, roan cattle are cattle that exhibit codominance of red and white
hair color alleles. Roan cattle have both red and white hairs expressed
FRFW. Which of the following cattle matings would produce the greatest
number of roan offspring:
Roan x Roan
Red x White
Red x Roan
White x Roan
Explain your answer.
All offspring would obtain a red allele from one parent and a white allele
from the other, so 100% roan offspring from these parents.
5. Checkered chickens are the result of codominance between the black
feather allele (CB) and the white feathered allele (CW). Can there be a truebreeding strain of checkered chickens? Explain why or why not.
No, since being checkered means that the chickens must be heterozygous
for the trait. Since they are CBCW, can’t be true breeding. Offspring of
two checkered chickens could inherit two CB alleles to be black or two CW
alleles to be white.
6. The curly hair (HC) and straight hair (HS) alleles exhibit codominance, to
produce a wavy hair phenotype for heterozygotes (HC HS). If a father has
straight hair, and a mother has wavy hair, what is the probability of
different hair phenotypes for their children?
Sperm
Egg
HC
HS
HS
HCHS
HSHS
HS
HCHS
HSHS
Phenotype Ratio: 1 wavy: 1 straight
Probability of Curly Hair: 0%
Probability of Wavy Hair: 50%
Probability of Straight Hair: 50%
7. Blood type in humans is a trait that exhibits multiple alleles. There are
three possible alleles for the main blood marker gene: IA, IB and i. Alleles
IA and IB exhibit codominance. The allele i, for blood type O, is recessive.
For each of the following blood type phenotypes, determine the possible
genotypes.
Phenotype
A
B
AB
O
Possible Genotypes
IAIA or IAi
IBIB or IBi
IAIB only
ii only
8. In a maternity ward, Mrs. Bright and Mrs. Light share a room. When they
are ready to go home, Mrs. Bright insists she has been given the wrong
baby. Analyze the blood type evidence below to see if it supports,
disproves or is inconclusive in this maternity issue.
Blood Types
Mrs. Bright
AB
Mr. Bright
O
Baby at Bright’s house
O
Mrs. Light
A
Mr. Light
A
Baby at Light’s house
A
Possible Genotypes
IAIB only
ii only
ii only
IAIA or IAi
IAIA or IAi
IAIA or IAi
Was there a mix-up of babies in the hospital? Explain your answer.
Yes, the Bright’s could not have a child with O blood, since the child
would have to receive an i (O) allele from each parent, and the
mother with does not have an i allele. The Light’s could have child
with blood type O, since each parent could have a hidden i allele.
9. What are the possible blood types of the offspring between a father who is
blood type AB and a mother who is blood type O.
A. AB or O
D. A, B, AB or O
B. A, B or O
E. A, B or AB
C. A or B
Explain your answer. Father could pass down either IA or IB. Mother always
passes down an i (O) allele
10. What are the possible blood types of the offspring between a father who
is blood type A and a mother who is blood type B.
A. AB or O
D. A, B, AB or O
B. A, B or O
E. A, B or AB
C. A or B
Explain your answer.
Each parent could have a hidden i allele. Therefore if IAi x IBi, all four
blood types could be produced.
In addition to the gene that controls the A, B, AB or O blood type, a second gene
in humans controls whether a person’s red blood cells have an Rh factor present.
Rh positive (R) is dominant over Rh negative (r).
Use the following information for questions 11-14. A woman who belongs to the
blood group A is Rh posititve. She has a daughter who is O positive and a son
who is B negative.
11. Which of the following is a possible genotype of the son?
A. IBIB rr
D. IBi rr
B
B
B. I I RR
E. IBIB Rr
C. IBi Rr
12. Which of the following is a possible genotype of the mother?
A. IAIA RR
D. IAi Rr
A
A
B. I I Rr
E. IAi RR
C. IAi rr
13. Which of the following is a possible phenotype for the father?
A. A negative
D. A positive
B. B negative
E. O positive
C. B positive
F. Either B or C
14. A man is brought to court for a paternity case. He has blood type B
positive. The mother has blood group B negative. The child has blood
type A negative. What can you say about the man’s chances of being the
father?
A. He is the father
C. He can not be the father
B. He might be the father D. He is unlikely to be the father