Plasmid DNA electrophoresis will have three bands, and the farthest one is linear DNA(lDNA): both strands of plasmid are broken; Linear molecule; In the middle is open-loop DNA(ocDNA): one strand of plasmid breaks; Relaxed cyclic molecules; * * * Valence Closed Loop DNA(cccDNA): The two strands of plasmid are not broken; Superhelix This is due to the mechanical force, pH, reagents and other reasons in the process of plasmid extraction, which leads to plasmid DNA strand breakage. Plasmid DNA is much smaller than genomic DNA, so it is easier to distinguish the 1 band of genomic DNA electrophoresis, although it will also break during your extraction, forming large fragments of tens to hundreds of kb. However, we usually use 1% glue. It is impossible to distinguish DNA of different sizes, so it looks like a belt. If lamda hindIII label is added to 0.6% gel and the running time is appropriately extended, several bands should appear.