In gel electrophoresis, DNA fragments move towards the positive electrode because
Correct answer: C. the phosphate groups of the backbone give DNA a negative charge
- A. they are heated during the run
- B. they carry no charge and drift at random
- C. the phosphate groups of the backbone give DNA a negative charge
- D. the gel pushes them mechanically
Explanation
Every nucleotide carries a negatively charged phosphate, so all DNA fragments move towards the anode, and the gel acts as a sieve in which short fragments travel further than long ones in the same time. This separates a mixture into bands by size alone. Comparing the pattern of bands between samples is the basis of DNA fingerprinting.
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