Question: the sickle-cell anemia allele is an example of the heterozygote advantage?
Answer: When a single copy of a disease allele doesn't result in a disease but instead is good for the person or organism that carries it, we say that allele has a heterozygote advantage. One example is sickle cell trait, which protects against malaria in heterozygotes, but causes a deadly disease in homozygotes.