In humans, sickle cell anemia is inherited as an incompletely dominant trait: in recessive homozygotes

| September 17, 2021 | education

In humans, sickle cell anemia is inherited as an incompletely dominant trait: in recessive homozygotes, severe anemia develops, which is usually fatal, and in heterozygotes, anemia manifests itself in a mild form. Plasmodium malaria cannot metabolize abnormal hemoglobin, so people with the sickle cell gene do not get malaria. In the family, both spouses have a mild form of anemia. 1) How many types of gametes does each spouse produce? 2) How many different phenotypes can there be among the children of this couple? 3) What is the probability (in%) of having a child with a severe form of anemia in the family? 4) What is the probability (in%) of having a child resistant to malaria? 5) What is the probability (in%) of having a malaria-resistant child in the family?

We write down “given”: the dominant gene (A) denotes a healthy person, recessive (a) – a patient with anemia, if a homozygote for a recessive trait (aa), then we designate it as a severe form of anemia, heterozygote (Aa) – a mild form of anemia, we also write down, that Father (♂) and mother have a mild form of anemia – Aa.

And what to find:

1) How many types of gametes does each spouse produce?

2) How many different phenotypes can there be among the children of this couple?

3) What is the probability (in%) of having a child with a severe form of anemia in the family?

4) What is the probability (in%) of having a child resistant to malaria?

5) What is the probability (in%) of having a malaria-resistant child in the family?

Then we write down the solution:

1.we write down parental genotypes (P): where the man is (♂) Aa, and the woman is also (♀) Aa

2. We paint gametes (G): both parents will produce two types of gametes A and a

3. We describe the offspring options (F): AA (healthy, not resistant to malaria), aa (Severe anemia, resistant to malaria), Aa (mild anemia, resistant to malaria), Aa (mild anemia, resistant to malaria )

We write down the answer to all the proposed questions:

1) 2 types of gametes

2) 3 phenotypes

3) 100% / 4 (number of genotypes) = 25% – AA

4) 100% – 25% = 75% – Aa, aa, Aa

5) 100% / 4 (number of genotypes) = 25% – AA



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