Which technique provides information about fragment sizes by comparison to a ladder?

• A. Agarose gel electrophoresis
• B. Sanger sequencing
• C. qPCR
• D. CRISPR editing

Answer: (A)

The technique relies on estimating fragment sizes by using a DNA ladder as a reference standard. In agarose gel electrophoresis, DNA fragments are separated in a gel by size: smaller pieces move faster and form bands at positions that correspond to their lengths. Running a DNA ladder, which contains fragments of known sizes, alongside your samples creates a reference map. By comparing where your sample bands line up with the ladder bands, you can approximate the fragment lengths present in the sample. This approach gives sizing information rather than sequence or quantity details and is widely used to verify PCR product sizes, digest fragments, or check insert lengths in plasmids.

Sanger sequencing, on the other hand, determines the exact nucleotide order of a DNA fragment, not its size by ladder. qPCR measures how much DNA is present in real time, not the exact fragment lengths. CRISPR editing is about making precise changes to a genome, not sizing DNA fragments.