Gel electrophoresis of DNA — Because DNA is negatively charged, it migrates through an agarose/polyacrylamide gel from which electrode toward which electrode?

Introduction:
Gel electrophoresis separates DNA fragments by size under an electric field. The direction of migration depends on the net charge of the molecule at the running pH and the polarity of the electrodes. This question checks understanding of basic electrophoretic principles for nucleic acids.

Given Data / Assumptions:

• DNA carries a net negative charge due to its phosphate backbone at neutral to basic pH.
• Electrophoresis setups place wells near the negative electrode so DNA migrates toward the positive electrode.
• Sieving through the gel matrix retards larger fragments more than smaller ones.

Concept / Approach:
Negatively charged DNA moves toward the anode (positive electrode). Electrode polarity, not acid–base labels, determines direction. Fragment length affects speed, not the sign of migration direction, which is fixed by charge.

Step-by-Step Solution:

Verification / Alternative check:
Loading dyes (e.g., bromophenol blue) co-migrate toward the anode, visually confirming direction during runs.

Why Other Options Are Wrong:

Common Pitfalls:
Placing the gel cassette backwards; loading wells near the anode causes DNA to run off the short edge.

Final Answer:
Negative to positive.