This DNA Ladder Diagram depicts a solution of different lengths of DNA molecules used in agarose or acrylamide gel electrophoresis. It is used as a reference to estimate the size of unknown DNA molecules separated using an electrical field through the gel. In routine molecular biology laboratories, the DNA Ladder Diagram is also used to determine the size of DNA fragments by electrophoresis. The DNA ladder is a standard-sized molecular marker or sequence of DNA fragments used to determine the extent of PCR amplicons. The bp next to each number shown in the ladder indicates the length of the DNA fragment in base pairs.