Methylation, histone marks and heritable expression states · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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How expression states persist through cell division

Science · Genetics & Evolution · ages 20-22
Name ______________________   Date ____________

  1. What effect is histone acetylation commonly associated with?

    • Less DNA access and transcription
    • Loss of the promoter DNA sequence
    • More DNA access and transcription

  2. In mammalian cells, increased CpG methylation at a promoter is often associated with which effect?

    • Often favors higher transcription
    • Often supports lower transcription
    • Often rearranges the promoter's DNA base sequence

  3. An epigenetic change can alter gene expression without changing the DNA base sequence.

    Circle one:   True   False

  4. Which process can help maintain histone states through DNA replication?

    • Reusing old histones and modifying new histones
    • Copying histone marks between DNA strands
    • Using DNA polymerase to copy the marked histone proteins

  5. After replication, a previously fully methylated CpG site has a methylated old strand and an unmethylated new strand. What helps restore methylation on both strands?

    • DNA polymerase adds methyl groups while copying the base sequence
    • DNMT1 helps methylate the corresponding new-strand site
    • Old-strand methyl groups move to the new strand

  6. In a hypothetical culture, a nutrient signal ends, but promoter methylation and low transcription persist through several cell divisions. Which interpretation respects the limits of these observations?

    • Persistence establishes that the nutrient signal caused a DNA sequence mutation
    • Maintenance methylation could help retain the promoter pattern
    • Persistence in daughter cells establishes inheritance by the organism's offspring

  7. A methylated promoter has measured low accessibility and low transcription despite an abundant activator. Which explanation fits these observations?

    • Activator abundance shows that promoter access is not limiting transcription
    • Limited promoter access can restrict activator binding
    • Low transcription identifies a change in the promoter's DNA base sequence

  8. A report gives only a quiet gene's base sequence and explicitly excludes DNA-modification and histone measurements. No mutation is found. A student says this rules out epigenetic regulation. What is overlooked?

    • Low transcription indicates a mutation
    • Matching base order indicates matching chromatin marks
    • The report did not measure the chromatin marks
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Answer key

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How expression states persist through cell division W1-mt_QIEjt77tjV-s1

  1. More DNA access and transcription · Histone acetylation often favors accessible chromatin and transcription. It does not guarantee that a gene will be transcribed.
  2. Often supports lower transcription · Promoter CpG methylation often supports repressor recruitment and lower transcription. It does not change the DNA base order.
  3. True · The statement is true. Epigenetic regulation can change expression while the DNA base sequence remains unchanged.
  4. Reusing old histones and modifying new histones · Parental histones are reused on daughter DNA, and enzymes modify newly added histones. Histone states are not copied directly between DNA strands.
  5. DNMT1 helps methylate the corresponding new-strand site · DNMT1 helps add methyl groups at corresponding CpG sites on the new strand. The old marks remain, and the base order does not need to change.
  6. Maintenance methylation could help retain the promoter pattern · Maintenance methylation could help preserve the promoter pattern. The observations do not establish that methylation caused low transcription.
  7. Limited promoter access can restrict activator binding · The measured low accessibility can restrict activator binding despite abundant activator. Methylation alone would not prove that the promoter is inaccessible.
  8. The report did not measure the chromatin marks · The report excludes DNA-modification and histone measurements. Finding no sequence change therefore does not rule out epigenetic regulation.
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