Final answer:
Sickle cell anemia is caused by a mutation where glutamic acid is replaced by valine in hemoglobin, causing cells to form a sickle shape and clog vessels, leading to various health issues.
Step-by-step explanation:
Sickle cell anemia is a genetic disorder characterized by the production of an abnormal type of hemoglobin, hemoglobin S. This condition arises due to a mutation in the gene encoding the β-globin chain of hemoglobin, where the hydrophilic amino acid glutamic acid is replaced by the hydrophobic amino acid valine at the sixth position. This seemingly minor change dramatically alters the hemoglobin's properties, leading to its aberrant self-association under low-oxygen conditions.
Within red blood cells, the mutated hemoglobin S molecules tend to aggregate, forming long, rigid fibers. These fibers distort the normal biconcave shape of the red blood cells into a sickle or crescent shape. These misshapen cells have increased difficulty passing through blood vessels, often blocking them and causing a multitude of symptoms, including severe pain and organ damage. Heterozygous individuals possess one sickle cell gene and one normal gene, often showing resilience to malaria but typically not the severe symptoms seen in those who are homozygous for the mutation.