This is a black-and-white photograph showing an agarose gel after electrphoresis.
Samples run are from PCRs on pGTλ clones, done by 2 groups of wet lab A students.
The PCR products would be used later on, as template for probe labeling for their Southern hybridisation experiment. This gel was meant to check the PCRs, which had been done on randomly chosen pGT
λ clones, which were made in a previous course.
μ>l of the 50μl PCR reactions were applied im the gel slots, and size markers (in lanes 1 and 12, contained 0.5μ
g Lambda DNA cut using EcoRI and BamHI (not heated prior to loading in the slots).

The students knew exactly the sizes of the Lambda fragments in the marker lanes, including the cos-site containing 9035 basepairs fragment (A).
Since the PCR products are just slightly bigger than the inserts in the pGT
λ clones (because the primers used were the pGT4-specific standard GeneTech primers), the students could easily recognise the inserts in the clones the chose as template for PCR:

PCR on pGTλ40 amplified apparently a 3240 bp insert (B); in the other lanes the inserts 1120 (C), 2752 (D), 4669 (E) and 3758 or 3775 (F) were detected. In all lanes it was clear, that the amount of products in the pCR reactions were very high; each 10ml sample contained more DNA (judged by eye..) than the biggest fragment in the marker lane. The water control showed no product as expected..

Another group of students choose 4 clones for PCR, and got the result shown in lanes 12 to 17.
PCR was successful for all four clones: inserts 3240 bp (G), 2752 (H), 2564 (I) and 3758 or 3775 (J) were recognised. But apparently, their MasterMix was contaminated with some DNA that gave a PCR product of about 1868 bp (K).