Answer: The frequency of the recessive allele increases
Explanation: The HbS gene is a variant of the B-globin gene which is responsible for sickle hemoglobin. There is a recessive disorder called sickle cell anemia that is caused by someone having two recessive alleles. When there's an outbreak of Malaria the frequency of the recessive allele of the HbS gene increases because people that are heterozygous have the advantage due to the fact they have normal and sickle hemoglobin so they are more resistant to malaria because malaria will only take action on normal hemoglobin.
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