Reversible, heritable changes called epigenetic factors also can indirectly regulate gene expression and protein production. These modifications can occur even without a change (mutation) in a gene's DNA sequence. Epigenetic alterations may be induced spontaneously, in response to environmental factors, or may simply be part of a person's genetic background. Some examples include:
- Addition of a methyl group to CpG dinucleotides, which are special regions in DNA bases where gene activity can be silenced when methyl groups are attached
- Removal of acetyl groups from histone tails, which stops the gene activity of the DNA bases wrapped around the histone, causing the DNA to coil up tightly.