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

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

• A. It provides fragments of known sizes to estimate the size of sample fragments.
• B. It stains DNA.
• C. It increases resolution.
• D. It acts as a loading dye.

Answer: (A)

The ladder serves as a ruler of known fragment lengths, run alongside the samples to size unknown DNA pieces. In gel electrophoresis, DNA bands migrate according to size, with smaller fragments moving farther. By comparing where each sample band lands relative to the ladder bands, you can estimate the length of the unknown fragments. This sizing works best when the ladder is run on the same gel under the same conditions and covers the size range of your samples. The ladder is not used to stain DNA, it doesn’t directly increase resolution, and it isn’t a loading dye. For example, if a sample band sits midway between the 1 kb and 2 kb ladder bands, you’d estimate around 1.5 kb.

The ladder serves as a ruler of known fragment lengths, run alongside the samples to size unknown DNA pieces. In gel electrophoresis, DNA bands migrate according to size, with smaller fragments moving farther. By comparing where each sample band lands relative to the ladder bands, you can estimate the length of the unknown fragments. This sizing works best when the ladder is run on the same gel under the same conditions and covers the size range of your samples. The ladder is not used to stain DNA, it doesn’t directly increase resolution, and it isn’t a loading dye. For example, if a sample band sits midway between the 1 kb and 2 kb ladder bands, you’d estimate around 1.5 kb.