in Fundamentals of Genetics by

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  1. Sickle cell anemia is caused due to the faulty gene HbS.
  2. The normal or healthy gene is HbA.
  3. When an individual is a heterozygote (HbS/ HbA) for the alleles, he/she is said to be a carrier.
  4. A carrier shows mild anemia as their RBCs become sickle shaped in oxygen deficiency.
  5. He/she is said to have sickle cell trait and are normal in normal conditions.
  6. However, an individual homozygous for HbS gene dies of fatal anemia.
  7. Sickle cell anemia is lethal in homozygous condition and produces sickle cell trait in carriers who are heterozygotes.
  8. Carriers are said to suffer from a milder form of anemia.
  9. Carriers produce sickle shaped RBCs as well as normal RBCs.

Hence, Sickle cell anemia is an example of incomplete dominance since neither of the two alleles are completely dominant over the other and the heterozygote is an intermediate.

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