Question

Marsha and Clement are both carriers of sickle cell anemia, a disease that is autosomal recessive. Their first child, Amelia, does not have the disease. Marsha and Clement are planning another pregnancy, but they are concerned about their second child having the condition. Clement’s father died from complications of sickle cell disease shortly before Amelia was born. 1. Draw a Punnett square to determine the likelihood of Marsha and Clement having a baby with sickle cell anemia. What is the chance the baby will be a carrier of the disease, just like the parents?

2. Marsha suggested to the nurse at the local family planning clinic that if the baby were a boy, he might have a higher risk of developing the disease, just like his grandfather. If you were this nurse, how would you respond?

3. When Amelia, who does not have sickle cell anemia, grows up and marries someone who does have the disease, how likely will her children have the disease?

Answer 1

1. 25% chance the baby will be born with sickle cell anemia (HbSS).

2. 50% chance the baby will be a carrier of the disease (HbAS), just like the parents.

3. 100% chance Amelia's children will be carriers of the sickle cell trait (HbAS) if their father has the disease (HbSS).

Problem 1: Punnett Square and Likelihoods

Parents' genotypes:

Marsha: HbAS (heterozygous carrier)

Clement: HbAS (heterozygous carrier)

Punnett Square:

HbA HbA

HbS HbAS HbAS

HbS HbAS HbAS

Each parent can pass on either HbA (normal) or HbS (sickle cell anemia) allele to their offspring.

The Punnett square shows all possible combinations of these alleles in the offspring.

There are 4 possible genotypes:

HbAS (carrier) - 50% chance

HbSS (sickle cell anemia) - 25% chance

HbAA (normal) - 25% chance

Therefore, there is a:

25% chance the baby will be born with sickle cell anemia (HbSS).

50% chance the baby will be a carrier of the disease (HbAS), just like the parents.

25% chance the baby will not have the disease or be a carrier (HbAA).

Problem 2: Responding to Marsha's Statement

Response to Marsha:

While it's true that Clement's father had sickle cell disease, the gender of the baby does not affect the risk of inheriting the disease. Both boys and girls have an equal chance of inheriting the HbS allele from either parent.

Sickle cell anemia is an autosomal recessive disease, meaning that both copies of the gene need to be mutated for the disease to manifest. The gender of the child does not play a role in this process.

Therefore, the risk of the baby having sickle cell disease is solely dependent on the parents' genotypes and the random segregation of alleles during meiosis.

Problem 3: Amelia's Children and Sickle Cell Anemia

Scenario:

Amelia (HbAA) marries someone with sickle cell anemia (HbSS).

Punnett Square:

HbS HbS

HbA HbAS HbAS

HbA HbAS HbAS

Amelia will always pass on the HbA allele to her children.

The father will always pass on the HbS allele to his children.

Therefore, all of Amelia's children will be carriers of the sickle cell trait (HbAS).