Before ligation, how does gel analysis help ensure the fragment is suitable?

Before ligation, how does gel analysis help ensure the fragment is suitable?

• A. Fragment size and integrity
• B. Concentration
• C. Purity by A260/A280
• D. Sequencing

Answer: (A)

The main idea here is that gel analysis is used to check the fragment’s size and whether it’s intact before ligation. Running the fragment on a gel shows a discrete band at the expected size if the DNA is the correct piece and still intact. A clean, single band suggests minimal degradation and that you’re working with the right fragment for ligation. If you see a smear or multiple bands, that signals degraded DNA or mixed fragments, which would lower ligation efficiency and lead to unwanted products. Other options aren’t the primary purpose of a gel in this step. Concentration is usually estimated or measured by other methods (like spectrophotometry or fluorometry), not by gel bands. Purity assessed by A260/A280 is a spectrophotometric measure of contaminants, not something you reliably read from a gel. Sequencing checks the actual sequence after cloning, not whether the fragment is the right size or intact for ligation.

The main idea here is that gel analysis is used to check the fragment’s size and whether it’s intact before ligation. Running the fragment on a gel shows a discrete band at the expected size if the DNA is the correct piece and still intact. A clean, single band suggests minimal degradation and that you’re working with the right fragment for ligation. If you see a smear or multiple bands, that signals degraded DNA or mixed fragments, which would lower ligation efficiency and lead to unwanted products.

Other options aren’t the primary purpose of a gel in this step. Concentration is usually estimated or measured by other methods (like spectrophotometry or fluorometry), not by gel bands. Purity assessed by A260/A280 is a spectrophotometric measure of contaminants, not something you reliably read from a gel. Sequencing checks the actual sequence after cloning, not whether the fragment is the right size or intact for ligation.