In a DNA gel image, if you see a band at the expected size, what does that indicate?

In a DNA gel image, if you see a band at the expected size, what does that indicate?

• A. The fragment of DNA of that size is absent.
• B. The fragment of DNA of that size is present.
• C. The ladder band indicates failure.
• D. The dye indicates sample purity.

Answer: (B)

In DNA gel electrophoresis, DNA fragments separate by size, and staining reveals bands where those fragments run. Seeing a band at the expected size means the specific fragment you were looking for is present in the sample. If that fragment weren’t there, you wouldn’t see a band at that position. The ladder provides reference sizes to estimate where bands should appear, but it isn’t a signal of failure. The dye helps visualize the gel and track migration, not assess the purity of the DNA.

In DNA gel electrophoresis, DNA fragments separate by size, and staining reveals bands where those fragments run. Seeing a band at the expected size means the specific fragment you were looking for is present in the sample. If that fragment weren’t there, you wouldn’t see a band at that position. The ladder provides reference sizes to estimate where bands should appear, but it isn’t a signal of failure. The dye helps visualize the gel and track migration, not assess the purity of the DNA.