After running a gel, how can you verify the presence of the fragment of the expected size?

After running a gel, how can you verify the presence of the fragment of the expected size?

• A. Measure absorbance with a spectrophotometer
• B. Compare to ladder and check for bands at the expected size; single band near expected size
• C. Sequence the gel
• D. Count the number of lanes

Answer: (B)

Verifying fragment size after a gel relies on comparing the observed DNA bands to a size ladder run on the same gel. If the fragment is present at the expected length, you’ll see a distinct band aligning with the corresponding marker on the ladder, ideally as a single sharp band indicating a single predominant fragment. Absorbance measurements don’t reveal size, only quantity. Sequencing the gel isn’t practical directly from the gel—you’d need to excise the band and sequence the DNA, which is a separate step. Counting lanes doesn’t provide information about fragment length or identity.

Verifying fragment size after a gel relies on comparing the observed DNA bands to a size ladder run on the same gel. If the fragment is present at the expected length, you’ll see a distinct band aligning with the corresponding marker on the ladder, ideally as a single sharp band indicating a single predominant fragment. Absorbance measurements don’t reveal size, only quantity. Sequencing the gel isn’t practical directly from the gel—you’d need to excise the band and sequence the DNA, which is a separate step. Counting lanes doesn’t provide information about fragment length or identity.