The normal allele of the ߖglobin gene, which produces a subunit for the oxygen-carrying hemoglobin, has two sites recognized by the Dde I restriction enzyme, which cuts the DNA into three restriction fragments.

The sickle-cell mutation destroys one of the Dde I restriction sites.

Digestion of mutant DNA with Dde I generates two fragments rather than the normal three.

These fragments can be identified by gel electrophoresis.