The spread of the sickle-cell allele among human populations differs from one region of the world to another. What explanation can account for this difference?
- APeople that are heterozygous for the sickle-cell allele have a resistance to cholera.
- BPeople that are heterozygous for the sickle-cell allele have a resistance to malaria.
- CPeople that are heterozygous for the sickle-cell allele are more likely to suffer from anaemia.
- DPeople with sickle-cell anaemia have more alleles.