PCR to DNA sequence

Once the polymerase chain reaction is complete and the target region has been amplified sufficiently, the sample is ready for additional assays that can analyse the region and look for any changes in the DNA code causing the patient’s phenotype. One of the most widely used assays is Sanger sequencing, named after the man who invented it, Frederick Sanger. In this method, the DNA is used as a template in order to generate a set of fragments that differ in length from each other by a single base. The bases at the end of each of these fragments are labelled with one of four different fluorescent dyes, one for each of the individual DNA bases.

The fragments are then separated by their size, and the bases at the end are imaged as they pass a high powered camera. This creates an image representing the original sequence of the DNA, known as an electropherogram. Because of the high quality of the data produced and the ability to characterise the DNA sequence at the molecular level, Sanger sequencing is currently the gold standard genetic test. The next section will show you how the reaction works in more detail.