In gel electrophoresis as a method for analyzing DNA, why is a DNA ladder (molecular weight marker) useful and why is it included on the gel?

• A. It provides DNA fragments of known sizes so you can estimate the base-pair lengths of sample bands by comparing migration distances.
• B. It ligates DNA fragments together to increase their size so they migrate more slowly and separate better.
• C. It prevents DNA degradation during electrophoresis by inhibiting nucleases in the gel matrix.
• D. It stains the DNA in the gel so sample bands become visible under UV light without any additional dye.

Answer: (A)

Verified step by step guidance

1. Understand the purpose of gel electrophoresis: it separates DNA fragments based on size, with smaller fragments migrating faster through the gel matrix than larger ones.
2. Recognize that the DNA ladder, also called a molecular weight marker, consists of DNA fragments of known and specific lengths (measured in base pairs).
3. Include the DNA ladder on the gel alongside your samples to serve as a reference for fragment size, allowing you to compare the migration distances of unknown DNA bands to the known sizes in the ladder.
4. By comparing the position of sample bands to the ladder bands, you can estimate the size of the DNA fragments in your samples, which is essential for analyzing and interpreting your results.
5. Note that the other options (ligating fragments, preventing degradation, or staining DNA) do not describe the function of the DNA ladder in gel electrophoresis.