Question

It is expected that selection pressure should have eliminated the gene for sickle cell anaemia. How would you account for its continuance in human population?

Answer 1

The sickle-cell allele is harmful in the homozygous condition, but heterozygous individuals gain resistance to malaria. In malarial regions, this survival advantage can outweigh the disadvantage of carrying one sickle-cell allele. Natural selection therefore maintains the allele in the population through heterozygote advantage.