Undigested DNA remains intact as a single, large molecule. It cannot move far down the gel matrix because of its large size, resulting in only one prominent band located closest to the loading wells. In standard diagrams , this is always represented by Lane 1.

Digested DNA (Lanes 2, 3, and 4) has been cleaved into multiple smaller fragments by restriction endonucleases. These smaller fragments experience less resistance moving through the gel and travel farther down, creating multiple distinct bands.

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