Question

Sol.(b) [Key Concept: Sickle Cell Trait — Malaria Protection] Sickle cell anaemia persists in African populations because the HETEROZYGOUS (carrier) state (HbA HbS) provides IMMUNITY AGAINST MALARIA. Carriers have sickle-shaped RBCs that are not supportive for the growth of the malarial parasite Plasmodium falciparum, conferring a survival advantage in malaria-endemic regions. This is called 'balanced polymorphism' or heterozygote advantage — the carrier state is actually beneficial, so the HbS allele is maintained in the population.