A way of identifying DNA fragments that have been cut with restriction enzymes (usually after they've been run on an electrophoresis gel) by eluting them onto a nitrocellulose filter or some other solid support, and then exposing them to radioactive or fluorescent DNA probes complementary to the sequences known or expected to be on the fragments being identified. The radioactive bands are then used to expose film, which will tell you where your DNA fragments were on the gel. In most setups, their position on the gel is directly related to the number of bases they have.

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