A methyl tag doesn't change the DNA sequence
- The idea
- Predict
- See it
- Why
- Check
The idea
“Methyl groups on a gene change or damage its bases, so it's a mutation.”
A methyl group is a real chemical change to DNA, so it's easy to call it a mutation. The order of the bases stays the same.
The short version
The mistake: Methyl groups on a gene change or damage its bases, so it's a mutation.
What's actually true: Marks on DNA or histones change whether a gene gets read. The base sequence stays exactly the same.
- A mutation changes the base sequence. An epigenetic change leaves the bases alone and changes how easily a gene is read.
- Methylation adds a small methyl group to cytosine. A heavily methylated control region keeps activators off, so the gene goes quiet.
- Histones can be marked too, which changes how tightly DNA is packed. Tightly packed genes are hard to transcribe.
- Cells copy methylation patterns when they divide, so a gene can stay off in daughter cells with no mutation.
On the exam: Tags on DNA or histones change whether a gene is read. Only a mutation changes the bases.