Gene Regulation and Epigenetics · USMLE Step 1

Which statement best describes how epigenetic modifications influence chromatin structure and gene expression?

  1. They change the DNA sequence to switch genes on or off
  2. They alter chromatin packaging and DNA accessibility, not sequence
  3. They always permanently and irreversibly inactivate a gene
  4. They act only transiently during early embryonic development
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Correct answer: They alter chromatin packaging and DNA accessibility, not sequence

Epigenetic modifications (DNA methylation, histone modifications, nucleosome remodeling) change chromatin structure and DNA accessibility to the transcription machinery, without altering the underlying DNA sequence.

Difficulty: Medium Question 7 of 20

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