What is a 50 bp DNA ladder?

A 50 bp DNA ladder is a mixture of DNA fragments used as a size standard or marker in agarose or polyacrylamide gel electrophoresis. Each fragment in the ladder is a specific number of base pairs (bp) in length, and when the ladder is run on a gel, each fragment forms a distinct band. By comparing the distance these bands move on a gel relative to the bands of an unknown sample, researchers can estimate the size of DNA fragments in their sample.

The "50 bp" in the name typically indicates that the fragments in the ladder are in increments of 50 base pairs or less. For instance, a common 50 bp DNA ladder might contain fragments of 50 bp, 100 bp, 150 bp, 200 bp, etc. The actual sizes of the fragments and the range they cover (e.g., from 50 bp to 500 bp, or 50 bp to 1500 bp) will depend on the specific ladder product.

When performing gel electrophoresis, researchers will load the DNA ladder into one of the wells in the gel. As the gel runs, the DNA fragments in the ladder will separate based on size, with smaller fragments moving further than larger fragments. This will produce a series of distinct bands on the gel, which can then be used as a reference to determine the size of unknown DNA fragments in other samples run on the same gel.