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).
Egg
CR / CWCR / CRCR / CRCW
CW / CRCW / CWCW
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 true-breeding 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?
Egg
HC / HSHS / HCHS / HSHS
HS / HCHS / HSHS
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 Possible Genotypes
A IAIA or IAi
B IBIB or IBi
AB IAIB only
O 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 Possible Genotypes
Mrs. Bright AB IAIB only
Mr. Bright O ii only
Baby at Bright’s house O ii only
Mrs. Light A IAIA or IAi
Mr. Light A IAIA or IAi Baby at Light’s house A 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. IBIB 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
B. IAIA 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