Question

The sickle-cell allele produces a serious blood disease in homozygous recessive individuals. why doesn't natural selection eliminate this allele from all human populations?

Answer 1

No, the sickle-cell anemia allele won't be eliminated by natural selection.

Sickle-cell anemia trait is controlled by a single gene and the allele (S) for sickle-cell anemia is a harmful autosomal recessive.

It is caused by a mutation in the normal allele (A) for hemoglobin (a protein on red blood cells).

Heterozygotes (AS) with the sickle-cell allele are resistant to malaria, a deadly tropical disease. It is common in many African populations.

In these areas, (S) carriers have been naturally selected, because their red blood cells, containing some abnormal hemoglobin, tend to be in sickle shape when they are infected by the malarial parasite.

Therefore, they are more likely to survive and reproduce. This keeps the S allele in the gene pool.

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