The first method of sequencing the genetic code was devised by Fred Sanger.
To sequence the DNA, it must first be separated into two strands.
This strand to be sequenced is copied using chemically altered basis.
These altered bases cause the copying process to stop each time one particular letter is incorporated into the growing DNA chain.
This process is carried out for all four bases,
and then the fragments are put together like a jigsaw to reveal the sequence of the original piece of DNA.