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BIO NMDCAT Structure of DNA
nmdcat.online July 3, 2026

99. A chemical mutagen modifies an adenine base within a gene via deamination, converting it into hypoxanthine. During subsequent rounds of DNA replication, hypoxanthine preferentially pairs with cytosine instead of thymine, resulting in a permanent

A. Transition mutation from an A-T pair to a G-C pair
✓
B. Transversion mutation from an A-T pair to a T-A pair
C. Frameshift mutation via single-nucleotide deletion
D. Nonsense mutation that halts transcription

📝 Explanation

Hypoxanthine pairs with cytosine, meaning the original template A-T pair becomes a G-C pair after a few rounds of replication, causing a transition mutation.

📖 Additional Information

  • Transition mutation from an A-T pair to a G-C pair
  • Transversion mutation from an A-T pair to a T-A pair
  • Frameshift mutation via single-nucleotide deletion
  • Nonsense mutation that halts transcription

Hypoxanthine pairs with cytosine, meaning the original template A-T pair becomes a G-C pair after a few rounds of replication, causing a transition mutation.

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