Question

You have two choices of DNA loading dye.

1: bromophenol blue or
2: xylene cyanol FF.
In TBE buffer, bromophenol blue runs at the same speed as a 370bp DNA fragment while xylene cyanol FF runs at the same speed as a 4160 bp DNA fragment. You have a PCR product which you expect to be 1000bp. Which loading dye would you use to add to your sample and run on the gel? Explain your answer.

Answer 1

For a PCR product expected to be 1000bp, bromophenol blue is the suitable DNA loading dye because it has a closer mobility to the expected DNA size and will thus provide better resolution on a gel.

Step-by-step explanation:

If you have a PCR product that you expect to be 1000bp, the appropriate DNA loading dye to use would be bromophenol blue. This dye runs at the same speed as a 370bp DNA fragment in TBE buffer, so it will provide a better resolution for distinguishing your 1000bp product on the gel.

On the other hand, xylene cyanol FF runs at the same speed as a much larger 4160bp DNA fragment and would move too slowly to be useful for tracking the migration of a 1000bp fragment during electrophoresis.