After the reactions, the fragments were separated by size on a denaturing polyacrylamide gel. An example of Maxam–Gilbert sequencing results is shown in Figure 9.2 . The sequence was inferred from the bands on the film. The lane in which that band appeared identified the nucleotide. Bands in the purine (G + A) or pyrimidine (C + T) lane were called based on whether they were also present in the G- or C-only lanes. In that way, the sequence was read from the bottom (5 ′ end of the DNA molecule) to the top (3 end of the molecule) of the gel.