Question

Q6. AFTER malaria is cured, the frequency of the HbS allele should decrease in regions with lots of mosquitoes because:

People will no longer die from sickle-cell anemia in these regions.

Having one copy of the HbS allele will no longer be advantageous in these regions.

Natural selection will no longer act on the HbS allele at all in these regions.

All alleles associated with genetic diseases eventually disappear.

Answer 1

After malaria is cured he frequency of the HbS allele should decrease in regions with lots of mosquitoes because natural selection will no longer be advantageous in these regions. Presence of HbS protects the population from malaria infection. In absence of the disease (malaria) there will not be any selection pressure to work on an allele that is mutated and likely to be not favoured by nature to exists. The prevalence of this allele in certain regions of the world coincides with the higher incedence of malaria as sickled RBC gives protection against the disease. However absence of the disease will remove the pressure that is essential to maintain an allele that produces a non functional hemoglobin.