Final answer:
The relative abundance of a DNA fragment in gel electrophoresis can be determined by comparing the intensity of bands on the stained gel, with darker or more intense bands indicating higher concentrations of the fragment.
Step-by-step explanation:
In gel electrophoresis, one can determine the relative abundance of a fragment by analyzing the intensity of the bands on the gel. The technique separates DNA, RNA, or protein fragments based on size. Smaller fragments travel further through the gel matrix, creating distinct bands at specific locations. By comparing the band intensities against a ladder of known concentrations, the relative abundance can be determined. This quantification can be achieved by the use of densitometry or by visual comparison if the difference is stark enough. Generally, the more concentrated a DNA fragment is within a sample, the more it will absorb the staining dye, and thus the darker or more intense the band will appear.
Using fluorescent dyes like ethidium bromide, scientists can visualize the separated fragments under ultraviolet light, allowing for the estimation of DNA fragment sizes and their relative quantities. Samples of known molecular weight (DNA ladders) are run alongside the target molecules to provide a size comparison, which helps in estimating the fragment sizes and their abundance.