In gel electrophoresis, what is the purpose of a DNA ladder?

In gel electrophoresis, what is the purpose of a DNA ladder?

• A. A DNA ladder provides size references to estimate fragment lengths.
• B. A ladder increases sample concentration.
• C. A ladder is used to digest DNA.
• D. A ladder binds to DNA to enhance amplification.

Answer: (A)

A DNA ladder provides a size reference in gel electrophoresis. It’s a mixture of DNA fragments with known lengths that you run in a separate lane so you can compare where your sample bands land. By matching the positions of your bands to the ladder bands, you can estimate the fragment sizes in base pairs or kilobases. This helps you verify if PCR products or restriction digests are the expected sizes. The ladder isn’t used to increase concentration, digest DNA, or enhance amplification.

A DNA ladder provides a size reference in gel electrophoresis. It’s a mixture of DNA fragments with known lengths that you run in a separate lane so you can compare where your sample bands land. By matching the positions of your bands to the ladder bands, you can estimate the fragment sizes in base pairs or kilobases. This helps you verify if PCR products or restriction digests are the expected sizes. The ladder isn’t used to increase concentration, digest DNA, or enhance amplification.