Dr. Thomas is having trouble explaining a procedure to his Korean-speaking patient.

Explanation: Why are there higher frequencies of the sickle cell allele in areas where malaria is more prevalent? In areas where malaria is endemic, the presence of the sickle cell allele in the heterogeneous state improves the fitness of individuals. However, convincing evidence indicates, in areas with persistent malaria outbreaks, individuals with the heterogeneous state have a distinct advantage (and this is why individuals with heterogeneous alleles are far more common in these areas). Those with the benign sickle trait possess a resistance to malarial infection.