What is the Function of a Ladder in Gel Electrophoresis?

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A ladder in gel electrophoresis is a mix of DNA fragments of known sizes used as a reference point in order to help estimate the size of unknown fragments that have been run on the same gel. A DNA ladder mixture consists of double-stranded DNA fragments with known fragment sizes ranging from 100–10,000 base pairs (bp). Each fragment size is labeled by a band; as the larger fragments migrate more slowly and will show up at higher positions along the gel, while shorter fragments migrate faster and are visible at lower positions on the gel.

The function of running ladders or molecular weight markers alongside samples is to enable an estimation of the sizes of molecules in a sample. After electrophoresis, researchers can use this system for measuring approximate size by comparing band position of samples to those which come from known markers or ladders. It also helps identify if there are problems with sample loading or gels that affect resolution and provides an internal control for ensuring consistent results between different experiments.

Without using DNA ladders it would be difficult to accurately determine the size or identify any breaks or mutations found within unknown specimens. Therefore, using ladders makes it possible for researchers to accurately measure DNA samples both qualitatively and quantitatively in their experiments.