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This lesson covers epigenetics — heritable changes in gene expression that do not involve changes to the DNA nucleotide sequence. This is a key topic in the Edexcel A-Level Biology specification (9BI0, Topic 7).
Epigenetics literally means "above genetics". It refers to modifications that affect gene expression without altering the underlying DNA sequence. These modifications can be:
The two main epigenetic mechanisms are DNA methylation and histone modification.
Exam Tip: The crucial distinction is that epigenetic changes alter gene expression (whether genes are switched on or off) without changing the base sequence of DNA. Mutations, by contrast, do change the base sequence.
To understand epigenetics, you need to understand how DNA is packaged in the nucleus.
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