How can I know whether there is any genomic DNA present in my purified plasmid?

 

Genomic DNA (gDNA) contamination can be observed if the sample lysate is treated too vigorously during the alkaline lysis and neutralization step.  gDNA can be identified by digestion of sample with EcoRI, which linearizes the plasmid. If there is any gDNA present, it shows as a smear on top of linear plasmid band.