DNA Electrophoresis & Fragment Separation — NEET Biology
✅ Asked in NEET 2025Which one of the following statements is incorrect regarding gel electrophoresis? (NEET 2025)
Which one of the following statements is incorrect regarding gel electrophoresis? (NEET 2025)
What is the criterion for DNA fragments movement on agarose gel during gel electrophoresis? (NEET 2017)
Answer & NCERT explanation
Correct answer: B — DNA moves towards cathode due to negative charge
DNA moves towards anode (positive electrode), not cathode, during gel electrophoresis because DNA has negative charge due to phosphate groups. The cathode is the negative electrode. All other statements are correct: DNA separates by size, agarose acts as sieving matrix, and ethidium bromide stains DNA. This is a fundamental concept in molecular biology techniques.
Read more NCERT concept on the PYQ
Separation and isolation of DNA fragments: The cutting of DNA by restriction endonucleases results in the fragments of DNA. These fragments can be separated by a technique known as gel electrophoresis. Since DNA fragments are negatively charged molecules they can be separated by forcing them to move towards the anode under an electric field through a medium/matrix. Nowadays the most commonly used matrix is agarose which is a natural polymer extracted from sea weeds. The DNA fragments separate (resolve) according to their size through sieving effect provided by the agarose gel. Hence, the smaller the fragment size, the farther it moves. Look at the and guess at which end of the gel the sample was loaded.
NTA tests whether students understand that DNA moves toward the anode in gel electrophoresis because DNA is negatively charged. Students often forget which electrode is anode or why smaller fragments move farther. The key trap: confusing the direction of movement or thinking larger fragments move faster. Remember: DNA always migrates toward the positive electrode (anode) due to its phosphate backbone's negative charge. Smaller fragments navigate through agarose pores easily, traveling farther, while larger fragments get trapped—this sieving effect is crucial. NEET asks both about the principle and practical details like where samples are loaded (negative end/cathode side).
What does NCERT say about Separation and isolation DNA?
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Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
88/90MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.