Question

Describe how natural selection can sometimes lead to the persistence of harmful or even lethal alleles. Include an example.

Answer 1

Heterozygosity of genes sometimes allows natural selection to maintain deleterious alleles. Sickle cell anemia is only exhibited by people who carry both alleles as recessive.
The recessive/recessive allele can become advantageous in a different environment or time. Sickle cell recessive allele protects their carrier against acquiring malaria.