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Cells can maintain differences in gene activity without changing the underlying base sequence. Explain the molecular mark and its regulatory consequence rather than calling every environmental effect a mutation.
Video by Cognito. The video’s own board label is retained; follow the specification reference and scope notes on this lesson for assessed content.
Viewing focus: Explain DNA methylation and histone acetylation
After watching, attempt these questions before opening the answers. You can also use the written lesson below.
After watching 1: In the stated syllabus model, reduced histone acetylation tends to:
Reduce transcriptional accessibility. Chromatin state affects access.
After watching 2: DNA methylation necessarily changes:
A chemical modification, not necessarily the base order. The distinction is central to epigenetic regulation.
What you'll be able to do
Eukaryotic DNA is associated with histones and other proteins. The organisation of this chromatin affects access by transcriptional machinery. In the syllabus model, reduced acetylation of associated histones can favour a less accessible state and reduce transcription.
DNA methylation adds chemical groups without replacing the base sequence. Increased methylation at appropriate regulatory regions can inhibit transcription. The effect depends on location and context, so a methylation measurement somewhere in a genome is not a universal instruction that every gene is switched off.
Epigenetics concerns changes in gene activity or function maintained through cellular inheritance without a corresponding base-sequence change. Regulatory marks can help preserve a differentiated cell’s expression pattern as it divides. Environmental conditions can influence some of these marks and the associated expression.
Inheritance through a cell lineage is not identical to guaranteed transmission through sexual generations. Many marks are reset during reproduction and development, and evidence for an intergenerational effect must address alternative genetic and environmental explanations. Avoid claiming that every acquired experience becomes permanently encoded for all descendants.
If a gene is methylated and expressed less, the observations show an association. Manipulating the mark, comparing suitable controls and measuring transcription can help test whether the change contributes causally. Differences in cell types within a sample can also affect the measured average.
Abnormal regulation can contribute to disease, including altered expression of genes controlling cell division. A proposed treatment that changes epigenetic regulation requires evidence about target genes, specificity, function and consequences elsewhere. A reversible mark does not guarantee that all resulting effects are immediately reversible or harmless.
Try each question before opening the worked response. Use precise biological terms, connect each cause to its effect, and check units and assumptions when interpreting data.
Common mistakes to avoid
Key takeaways
Check the assessed scope and practical or mathematical requirements.
An external explanation or interactive activity to use alongside the lesson. It may include extension material.
Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.
Test yourself
Answer a few questions, then review anything you missed.
Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.