Amgen Biotech Experience (ABE) Lab Practice Test

Troubleshooting why a sample lane shows no bands while the ladder shows bands. When the ladder in a gel runs and bands are visible but the sample lane is blank, the issue is likely with the sample itself rather than the gel or staining. This points to problems during sample preparation or loading, or the template/DNA quality. If the DNA has degraded, there may be no intact fragments to visualize, or the fragments may be too small or irregular to produce clear bands. If loading was missed or the sample wasn’t actually loaded into the well, there would be no signal in that lane despite a working ladder. Checking that the DNA was properly prepared, that the DNA is intact and at a detectable concentration, and that the loading step was performed correctly (including using loading dye and pipetting into the correct well) addresses the issue. The other options don’t fit because a gel that can reveal ladder bands indicates the system is capable of visualizing DNA, so claiming the gel isn’t suitable isn’t consistent. If the ladder runs, the problem isn’t that the ladder caused the sample to run off, and a DNA concentration that’s too high typically causes smearing or overloading rather than a complete absence of bands in the sample lane.