Final answer:
Histone modifications, such as acetylation and methylation, can regulate gene transcription by altering the chromatin structure. These modifications affect the accessibility of DNA and the recruitment of proteins involved in transcription.
Step-by-step explanation:
Epigenetic changes, such as histone modifications, can regulate gene transcription by altering the chromatin structure. Histone proteins can be chemically modified through processes like acetylation, de-acetylation, methylation, and phosphorylation. For example, acetylation of certain lysine residues in histones H2B and H4 tends to open up the chromatin and promote transcription, while methylation can either open or close the chromatin depending on the specific lysine or arginine residue that is methylated. These modifications affect the accessibility of the DNA and the recruitment of other proteins that can activate or block transcription.