Separation and isolation of DNA fragments

DNA fragments obtained by restriction digestion are separated by gel electrophoresis.
The most commonly used matrix is agarose, a natural polymer extracted from sea weeds.
DNA fragments, being negatively charged, move towards the anode through the agarose gel, which acts as a sieve, so they separate according to their size.
Spectrophotometry and PCR do not use agarose; tissue culture media are solidified with agar, not purified agarose.
Hence agarose finds use in gel electrophoresis.

Cutting of DNA by restriction endonucleases results in fragments of DNA, which are separated by a technique known as gel electrophoresis.
DNA fragments are negatively charged molecules, so they move towards the anode under an electric field through a medium or matrix.
The most commonly used matrix is agarose, a natural polymer extracted from sea weeds.
The DNA fragments separate (resolve) according to their size through the sieving effect provided by the agarose gel: the smaller the fragment, the farther it moves.
The separated bands are seen as bright orange bands after staining with ethidium bromide and exposure to UV radiation.
Cutting of DNA is done by restriction enzymes and joining by DNA ligase, not by electrophoresis.
So gel electrophoresis is used for the separation of DNA fragments according to their size.