making a copy of the DNA

The technique relies on making a copy of the DNA in
the presence of modified versions of the four bases (A, C, G,
and T) which are fluorescently labelled with their own specific
tag. The sequencing products are then separated with the use
of long polyacrylamide gels with a laser being used to
automatically detect the fluorescent molecules as they migrate.
A computer program is then used to generate the DNA
sequence. Recent improvements in DNA sequencing have seen
polyacrylamide gels being replaced by capillary columns
allowing the method to be further automated.