<unk>  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 cells). Sickle cell disease is a blood disorder wherein there is a single amino acid substitution in the hemoglobin protein of the red blood cells, which causes these cells to assume a sickle shape, especially when under low oxygen tension. Sickling and sickle cell disease also confer some resistance to malaria parasitization of red blood cells, so that individuals with<unk>  (heterozygotes) have a selective advantage in environments where malaria is present.
Sickle cell trait
Sickle cell disease
Sick cell syndrome
Hereditary spherocytosis
Paroxysmal nocturnal hemoglobinuria
EEM syndrome
Primary hyperoxaluria
Hemoglobinemia