Isolate/purify nucleic acid: digest (or not, depending on question and fragment source, i. e. genomic. Dna, plasmid dna, pcr amplicons: resolve fragments by agarose gel electrophoresis, detect band patterns and analyze data via direct uv staining or. Southern blot: agarose gel electrophoresis is uses to assess the size of dna fragments, gels are stained with an intercalating agent often ethidium bromide, uv light allows for visualization of the ethidium bound dna. Southern blotting: less common with advanced pcr and genome-sequencing technologies, still useful for analyzing single or multiple gross genetic changes (deletion mutants, insertion mutants, based on dna/dna hybridization. Size and elution are linearly related, and gel filtration can be used to estimate molecular weight. Dnas and rnas are sometimes analyzed using polyacrylamide instead. Logarithmic relationship between molecular mass and electrophoretic mobility. Immunoblot (western blot) can do this it can detect trace amounts of specific proteins: requires an antibody to the protein or the tage, does not provide information regarding purity.