Natural Selection Can Maintain Genetic Variation by Favoring Heterozygous Genotypes

Essay

Natural selection can maintain genetic variation by favoring heterozygous genotypes.In equatorial Africa,the best genotype to have for hemoglobin is heterozygous (HbA / HbS).In the United States,there is no advantage to the heterozygous genotype.HbA codes for normal hemoglobin,whereas HbS codes for abnormal hemoglobin that causes red blood cells to become distorted in shape (sickle cell).Explain why the heterozygous state is advantageous in Africa,but not in the United States.What has happened to the sickle-cell allele in Africa? What has happened to the sickle-cell allele in the United States?