The one responsible for maintain the presence of this allele in the population’s gene pool is the heterozygote advantage. It is because the advantage of having this for a sickle cell disease is that if a person has a strong heterozygote advantage and that he or she has a copy of the allele that cause the sickle cell disease, the person will likely be resistant to the disease because of the heterozygote advantage in which the heterozygote genotype has a higher relative fitness making it resistant to the disease.
