Restriction enzymes and sequencing 2. The migration of a DNA fragment depends on its size.
Small fragments migrate faster than big fragments.
This means that a fragment of 500 bp is separated better from a 1 kb fragment, than a 3 kb fragment is separated from a 3.5 kb fragment. Better separation equals larger space between the fragments. Restriction enzymes can be used to make maps of a given piece of DNA, with the restriction sites providing the landmarks. Having a map is useful for recombinant DNA technology. A schematic representation of a gel is shown below.