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Unformatted text preview: its supply of oxygen, and rbcs die- leads to severe anemia, weakness Homozygous SS genotype normally lethal; mortality by age 15 when untreated A codominant gene system o 3 genotypes: AA-normal rbcs, AS- heterozygous for sickling, SS- homo for sickling o AA: normal, AS- normal except under oxygen stress or heavy workload, as at high altitudes, SS- severely anemic, enlarged spleen, early mortality without major western medical intervention Frequency of the S allele in some areas of coastal west Africa>20%. o Why hasnt natural selection eradicated the S allele? Malaria!!...
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- Fall '08