Methylation of the promoter and histones in nucleosomes as examples of epigenetic tags
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Question
Define epigenetics.
Answer
**Heritable changes in gene expression** that do **NOT change the DNA base sequence**.
Question
What does DNA methylation do to a gene?
Answer
Methyl (**CH₃**) groups are added to the DNA (often at the **promoter**), which **blocks transcription** and **silences** the gene (switches it OFF).
Question
How does histone modification control gene expression?
Answer
It changes how **tightly the DNA is packed**: **tightly packed = OFF** (hidden from RNA polymerase), **loosely packed = ON** (accessible).
Question
Tightly packed DNA — is the gene ON or OFF?
Answer
**OFF** — condensed DNA is inaccessible, so RNA polymerase cannot reach the gene.
Question
How is an epigenetic change different from a mutation?
Answer
A **mutation changes the base sequence**; an **epigenetic** change only changes **whether the gene is expressed** — the sequence is unchanged.
Question
Are epigenetic marks permanent?
Answer
No — they are **reversible**, and they can also be **inherited** (copied to daughter cells).
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Gene expression
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