Final answer:
Not mixing DNA samples with a loading dye before gel electrophoresis would result in poor sample loading and difficulty tracking the electrophoresis progress, risking poor DNA separation or losing DNA off the gel.
Step-by-step explanation:
Two major problems would occur if DNA samples are not mixed with a loading dye before loading them into gel wells during gel electrophoresis.
First, without the dye, which increases the density of the sample, the DNA solution could be too light and could diffuse out of the wells rather than sinking into them, leading to poor resolution of DNA bands.
Second, the loading dye contains tracking dyes that move at predictable rates and help in monitoring the progress of the electrophoresis process, enabling the researcher to know when to stop the run.
Without these, it can be difficult to track the migration and risk the DNA to either not running enough or running off the gel.