The 1 Kb DNA Extension Ladder is suitable for sizing linear double-stranded DNA fragments from 500 bp to 40 kb. The ladder consists of 8 fragments ranging in length from 1,018 to 8,144 bp in 1,018-bp increments, as well as bands of 506 bp, 517 bp, 1,636 bp, 10 kb, 15 kb, 20 kb, and 40 kb. For easy reference on agarose gels, the 5 kb band is two to three-times brighter than the other bands in the ladder. This ladder can be stained with ethidium bromide or radiolabeled using T4 polynucleotide kinase, T4 DNA polymerase, DNA polymerase I, or the large fragment DNA polymerase I (Klenow fragment).