An Actual Gel Picture
Here is an actual photograph from a PCR experiment screening a DNA library for a specific barley sequence (Figure: Photograph). In this picture the first lane contains a molecular weight marker. Lanes #2 and 9 show DNA samples which contain the gene of interest. Lanes #12 and 13 represent a positive control, where the barley DNA sequence was already known to be present before doing the PCR. All other lanes represent DNA samples which do not contain the barley sequence because no bands are seen.