Restriction fragment analysis.

The normal allele of the beta-globin gene, which produces a subunit for hemoglobin, has two sites recognized by the Dde I restriction enzyme, yielding 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, yielding a restriction fragment length polymorphism (RFLP).

These fragments can be identified by gel electrophoresis.