Sickle Cell (Mendelian Genetics Probability WS)
2. c. What are the chances that any one of this couple's children will have sickle cell disease?
0%
1.a. What is the chance that a child will carry the HbS gene but not have sickle cell disease?
1/2
2. d. If this couple lives in the lowlands of East Africa, what are the chances that one of their children would be resistant to malaria if exposed to the malaria parasite?
1/2
3. e. What are the chances that any one of this couple's children will have sickle cell disease?
1/2
5.a. What are the chances that a child of this couple will have type B blood and sickle cell trait? (Show your work.)
1/2 × 1/2 = 1/4
1. c. What are the chances that these parents will have three children who have both normal and mutant hemoglobin beta chains? (Show your work.)
1/2 × 1/2 × 1/2 = 1/8
1. e. What are the chances that these parents will have two children with sickle cell trait and one with sickle cell disease? (Show your work.)
1/2 × 1/2 × 1/4 = 1/16
5.c. What are the chances that a child will have type B blood and sickle cell disease? (Show your work.)
1/2 × 1/4 = 1/8
5.d. What are the chances that a child will have type B blood and at least some normal hemoglobin?(Show your work.)
1/2 × 3/4 = 3/8
1. b. What are the chances that these parents will have three children who are homozygous for normal RBCs? (Show your work.)
1/4 × 1/4 × 1/4 = 1/64
1. d. What are the chances that all three of their children will show the disease phenotype? (Show your work.)
1/4 × 1/4 × 1/4 = 1/64
5.b. What are the chances that a child will have type AB blood and will not have sickle cell disease? (Show your work.)
1/4 × 3/4 = 3/16
1. f. In the cross above, if you know that the child does not have sickle cell disease, what is the chance that the child has sickle cell trait?
2/3
4. c. Complete the dihybrid Punnett square to determine the frequency of the different phenotypes in the offspring. (Note: Consider blood type and normal versus mutant hemoglobin in the various phenotypes.)
3/16 Blood type A, normal hemoglobin (normal RBCs) 3/8 Blood type A, normal and mutant hemoglobin (sickle cell trait) 3/16 Blood type A, mutant hemoglobin (sickle cell anemia) 1/16 Blood type O, normal hemoglobin (normal RBCs) 1/8 Blood type O, normal and mutant hemoglobin (sickle cell trait) 1/16 Blood type O, mutant hemoglobin (sickle cell anemia)
3. c. What is the genetic makeup of the gametes the father can produce?
A or S
2. a. What are the genotypes of the parents?
AA and AS
7.b. What are the possible genotypes of the father in the first generation?
AA or AS
7.f. What is the possible genotype or genotypes of the mother in the second generation?
AA or AS
6.a. What is the genotype of the father in the first generation?
AS
3. a. What are the genotypes of the parents?
AS and SS
6.c. What is the genotype of individual 3 in the second generation? How do you know?
AS; he and his son do not have sickle cell anemia, so he has at least one normal hemoglobin gene (A). He also has a son with sickle cell disease (SS). Therefore, he must carry one mutant hemoglobin gene (S) in order to have passed it on to his son.
7.c. What can you say about the genotype of all the children of the couple in the first generation? Explain your answer.
All the children in the second generation are heterozygous (AS) for the sickle cell allele. None of the children have sickle cell disease, so they possess at least one normal hemoglobin gene (A). Each child would have inherited the mutant hemoglobin gene (S) from the mother, because she has sickle cell anemia (SS).
4. b. What are the genetic makeups of all the possible gametes they can produce?
I^A A, I^A S, i^O A, or i^O S
4. a. What is the genotype of the parents?
I^A i^O AS
2. b. In a Punnett square, show all the possible genotypes of their children. State the genotype and phenotype ratios of the offspring
Genotype Ratio AA: 50% AS: 50% Phenotype Ratio 50% normal hemoglobin (normal RBCs):50% normal and mutant hemoglobin (sickle cell trait)
3. d. In the Punnett square, show all the possible genotypes of their children. Then summarize the genotype and phenotype ratios of the possible offspring
Genotype Ratio 50% AS: 50% SS Phenotype Ratio 50% normal and mutant hemoglobin (sickle cell trait): 50% mutant hemoglobin (sickle cell disease)
7.g. If the couple in the third generation has another child, what are the child's chances of the following?
Having sickle cell disease 1/4 Having sickle cell trait 1/2 Being homozygous for normal RBCs 1/4 Being resistant to malaria and not having sickle cell disease 1/2
3. f. If this couple moves to the lowlands of East Africa and has children, which of their children would be more likely to survive? Explain your answer.
If this couple moves to the lowlands of East Africa, the family would be exposed to the Anopheles mosquito that transmits the Plasmodium parasite, which causes malaria. Children who have sickle cell disease (SS) have a lethal disease and will be less likely to survive regardless of where they live. Children with sickle cell trait (AS) have two advantages: they have a greater resistance to malaria, and they normally do not show symptoms of sickle cell disease. Therefore, heterozygotes are more likely to survive.
7.e. What are the genotypes of the parents in the third generation? Explain how you know
Mother AS Father AS Neither parent has sickle cell anemia, so each parent possesses at least one normal hemoglobin gene (A). They do have children with sickle cell anemia (SS), so each must possess at least one mutant hemoglobin gene to pass on to their children.
6.e. If the entire family moves to the lowlands of East Africa, four of the five males in the pedigree will have two genetic advantages over the other individuals in the family. Explain the two advantages.
Moving to the lowlands of East Africa exposes this family to mosquitoes carrying the Plasmodium parasite. Therefore, the four males who are heterozygous (AS) for the sickle cell allele have two distinct genetic advantages. First, they don't suffer from sickle cell disease. Second, they are more resistant to malaria infection due to their heterozygous genotype.
1. If two people with sickle cell trait have children, what is the chance that a child will have normal RBCs in both high- and low-oxygen environments? What is the chance that a child will have sickle cell disease? Write the possible genotypes in the Punnett square.
Normal RBCsin high- and low-oxygen environments 1/4 Sickle cell disease 1/4
3. b. What is the genetic makeup of the gametes the mother can produce?
S
6.b. What is the genotype of the daughter in the second generation?
SS
7.a. What is the genotype of the mother in the first generation?
SS
6.d. If the couple in the second generation has another child, what are the chances that the child will have the following?
Sickle cell disease 1/2 Sickle cell trait 1/2 Completely normal hemoglobin 0%
7.d. Regarding the answer to Question 7c, based on where the family resides, why would this genotype be considered a disadvantage?
This family lives in New York City, which has a very low prevalence of malaria infection, so their AS genotype confers no genetic advantage. For the most part, the heterozygous genotype in New York City confers no distinct advantage or disadvantage. However, if any of these individuals mated with another heterozygous (AS) individual, they would have a 25% chance of having children with sickle cell anemia, which can be a deadly disease. The disadvantage of the AS genotype is in the possibility of future generations having sickle cell disease.
