The persistence of the sickle-cell anemia allele in some African populations is the result of ____
a. a high rate of mutation of the normal allele to the sickle-cell anemia allele
b. the advantage of the heterozygous form over the homozygous forms
c. nonrandom mating
d. a decline in the occurrence of malaria in Africa
e. genetic drift
ANSWER: b
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