It is a well-known tool of gene analysis and is not experimental. Correctly done, DNA doesn't lie. I guess you can tell I watched a lot of the Simpson Trial. The DNA fragments are then placed near one end of a bed of gel that has an electric current running through it. The DNA is negatively charged and moves to the positive end of the gel.
Smaller fragments move faster than large ones.
After about 18 hours, the fragments are arranged by length. This procedure is called electrophoresis. These splits are transferred to a nylon membrane. The nylon membrane is immersed in a bath and a radioactive probe. The probe is actually a stretch of DNA of a known sequence.