The 25 bp DNA Ladder is suitable for sizing double-stranded DNA from 25 bp to 500 bp. Prepared from a plasmid containing repeats of a 25 bp DNA fragment, the ladder consists of 19 blunt fragments ranging in length from 25 to 450 bp, at 25 bp increments, plus a 500 bp band. This ladder can be stained with ethidium bromide or radiolabeled using T4 DNA polymerase or T4 polynucleotide kinase.