What is the purpose of a DNA ladder in gel electrophoresis?

What is the purpose of a DNA ladder in gel electrophoresis?

• A. Stain DNA during running.
• B. Estimate the sizes of DNA fragments by comparing to known fragment lengths.
• C. Determine the concentration of the DNA sample.
• D. Serve as a loading dye for the gel.

Answer: (B)

A DNA ladder acts as a size standard in gel electrophoresis. It provides a set of DNA fragments with known lengths that run in the same gel as your samples. By comparing where the sample bands appear to the positions of the ladder bands, you can estimate the sizes (in base pairs or kilobases) of the sample fragments. This reference makes it possible to determine if a fragment is, for example, within a specific size range or matches an expected length. The ladder isn’t primarily for staining DNA, determining concentration, or serving as a loading dye, though many ladders are run with loading dyes to help track the run.

A DNA ladder acts as a size standard in gel electrophoresis. It provides a set of DNA fragments with known lengths that run in the same gel as your samples. By comparing where the sample bands appear to the positions of the ladder bands, you can estimate the sizes (in base pairs or kilobases) of the sample fragments. This reference makes it possible to determine if a fragment is, for example, within a specific size range or matches an expected length. The ladder isn’t primarily for staining DNA, determining concentration, or serving as a loading dye, though many ladders are run with loading dyes to help track the run.