Choose the correct answers from the alternatives given.
The continued occurrence of sickle-cell disease in parts of Africa with malaria is due to

The correct option is C Fitness of the heterozygote
Sickle cell anemia is an inherited blood disease where red blood cells show an abnormal crescent (or sickle) shape. It is an autosomal recessive disease in which one gene of allele codes for a normal protein and the other one codes for defective hemoglobin (sickle-celled).

Heterozygous individuals ie., carrying just one copy of the sickle mutation (inherited from either the father or mother), do not develop sickle cell anemia. However, such individuals are protected against malaria. This defective hemoglobin cause sickling of RBC in which malarial parasite cannot survive. This explains the high prevalence of this mutation in parts of Africa, where malaria is endemic.

So the correct answer is "Fitness of the heterozygote"