What indicates a DNA ladder is functioning properly in a gel run?

What indicates a DNA ladder is functioning properly in a gel run?

• A. Distinct, evenly spaced bands corresponding to known fragment sizes.
• B. A single smeared band across lanes.
• C. No bands in the ladder lane.
• D. Random fluorescence.

Answer: (A)

A DNA ladder acts as a size standard in gel electrophoresis, so its proper functioning is shown by multiple distinct bands at known fragment sizes that appear in evenly spaced steps along the lane. These clear bands provide reference points to estimate the sizes of sample DNA fragments, because fragment migration is predictable by size. If you instead see a single smeared band, no bands, or random fluorescence, that signals problems with loading, running the gel, staining, or ladder integrity, and you wouldn’t be able to confidently size the samples.

A DNA ladder acts as a size standard in gel electrophoresis, so its proper functioning is shown by multiple distinct bands at known fragment sizes that appear in evenly spaced steps along the lane. These clear bands provide reference points to estimate the sizes of sample DNA fragments, because fragment migration is predictable by size. If you instead see a single smeared band, no bands, or random fluorescence, that signals problems with loading, running the gel, staining, or ladder integrity, and you wouldn’t be able to confidently size the samples.