Question

The disease, sickle-cell anemia is common in malaria-infested areas because individuals that are heterozygous for the gene (AS) have enhanced resistance to malaria over normal individuals (AA). Individuals with severe sickle-cell anemia (SS) usually die before reproduction. If this population moves to an area without malaria, what will happen to the allele frequency of the A allele over time?

1) It will go up because there is no sickle cell anemia.
2) It will go up because there is no malaria.
3) It will go down because there is no malaria.
4) It will go down because there is no sickle cell anemia.

Answer 1

In an area without malaria, the selective pressure for the sickle cell allele (S) is absent, leading to an increase in the frequency of the normal A allele over time.

Step-by-step explanation:

If a population with a high frequency of the sickle cell allele (S) moves to an area without malaria, the selective pressure that maintained the S allele due to its protective effects against malaria would be absent. Thus, over time, because the heterozygote advantage (AS) is no longer beneficial, the frequency of the A allele is likely to increase. Individuals with the severe sickle-cell anemia (SS) have reduced fitness as they often die before reproduction, meaning the S allele would decrease in frequency without the balancing effect of malaria resistance.

The correct answer to the question is that the frequency of the A allele will go up because there is no malaria (option 2).