Sickle cell trait

Common card · No. 239940

Sickle cell trait describes a condition in which a person has one abnormal allele of the hemoglobin beta gene (is heterozygous), but does not display the severe symptoms of sickle cell disease that occur in a person who has two copies of that allele (is homozygous). Those who are heterozygous for the sickle cell allele produce both normal and abnormal hemoglobin (the two alleles are codominant with respect to the actual concentration of hemoglobin in the circulating). Sickle cell disease is a blood disorder in which a single amino acid substitution in hemoglobin can cause red blood cells to become sickle-shaped, especially under low-oxygen conditions. Sickling confers some resistance to malaria parasitization of red blood cells, so that individuals with sickle-cell trait (heterozygotes) have a selective advantage in environments where malaria is present.

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