Putting DNA to Work

Sickle Cell Anemia

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What Difference Do the Letters Make?

The gene defect that causes sickle cell anemia involves just one letter. And this small change in the sequence has an enormous impact on health.

Human chromosomes with HBB gene labeled

One of the genes that codes for part of hemoglobin, the molecule that carries oxygen through the bloodstream, is mutated in individuals with sickle cell anemia. Normal hemoglobin fits into round-shaped red blood cells, which move smoothly through tiny capillaries to nourish muscles, organs, and other tissues. The single-letter sickle cell mutation causes hemoglobin molecules to cluster together, forming long, rod-like structures. These structures cause the red blood cells to become stiff and assume a characteristic sickle shape. Sickle-shaped red blood cells stack up, causing blockages that starve the body’s tissues of oxygen. The resulting illness is known as sickle cell anemia.

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