Final answer:
Histone tail methylation typically results in chromatin compaction which makes DNA less accessible for transcription, though effects can vary depending on the specific modifications and contexts.
Step-by-step explanation:
Methylation of histone tails can have different effects on the accessibility of DNA, but it commonly leads to chromatin compaction, making DNA less accessible for transcription. This involves the addition of methyl groups to certain amino acids in the histone tails, which causes the chromatin to become more tightly packed. These modifications do not change the DNA sequence itself but instead influence how tightly the DNA is wrapped around histone proteins. For instance, methylation of specific lysines in histone H3 can repress transcription. Conversely, in some contexts, histone methylation can lead to a more open chromatin structure, enhancing gene expression. However, such modifications, including histone acetylation and deacetylation, can also influence DNA accessibility and gene expression, sometimes leading to opposing effects.