Final answer:
Heterozygosity for the sickle cell allele provides resistance to malaria, allowing carriers to have a survival advantage in malaria-endemic regions
Step-by-step explanation:
Heterozygosity for Sickle Cell Disease (SCD) is beneficial in regions where malaria is prevalent because individuals with one copy of the sickle cell allele, known as heterozygous (AS), have a natural resistance to the malaria parasite.
Hemoglobin S, the abnormal hemoglobin variant that causes SCD, is associated with this protective effect against malaria. The presence of Hemoglobin S in red blood cells creates an environment that is less hospitable to the malaria parasite, preventing it from completing its life cycle and consequently protecting the carrier against the disease
This natural resistance maintains the prevalence of the S allele in the gene pool in these areas, even though having two copies of the allele can cause severe sickle cell disease without the protective effect.