The presence of the sickle-cell trait (heterozygous \( \text{Hb}^A / \text{Hb}^S \)) offers partial protection against malaria, which is why it is more common in regions where malaria is endemic.
Coupling that is less prone to malaria refers to heterozygous individuals who have one normal hemoglobin allele (\( \text{Hb}^A \)) and one sickle cell allele (\( \text{Hb}^S \)). This is known as the genotype \( \text{Hb}^A / \text{Hb}^S \), also referred to as the sickle cell trait. Here's why:
Sickle Cell Trait (\( \text{Hb}^A / \text{Hb}^S \)): Individuals with this genotype are considered to have a balanced advantage; they are typically healthy because they largely produce normal hemoglobin, which prevents sickling under low oxygen conditions. Importantly, this genotype provides a protective effect against malaria, especially in regions where malaria is prevalent. The presence of some sickle-shaped cells reduces the parasite's ability to survive and multiply.
Normal Hemoglobin (\( \text{Hb}^A / \text{Hb}^A \)): Individuals with this genotype do not have the sickle cell trait and thus do not have any natural resistance to malaria.
Sickle Cell Disease (\( \text{Hb}^S / \text{Hb}^S \)): Individuals with this genotype suffer from sickle cell disease, which can be detrimental to health, causing severe anemia and painful crises. While this group may have resistance to malaria, the health consequences outweigh the benefits.
Conclusion: The genetic advantage of \( \text{Hb}^A / \text{Hb}^S \) arises because individuals remain largely unaffected by the sickle cell disease while gaining partial immunity to malaria.
Therefore, the correct choice is \( \text{Hb}^A / \text{Hb}^S \).
