CSEC Biology · May/June 2016 · Paper 2 · Question 6(b)(iii)

Sickle-cell anaemia is caused by the presence of a recessive allele. Persons who are heterozygous and carry the sickle-cell allele are more resistant to a type of severe malaria than persons who are homozygous for the normal haemoglobin allele.

Explain why the sickle-cell allele is more common in the population, in countries where the severe form of malaria is present.