Final answer:
Modification of chromatin structure through epigenetic changes like acetylation and methylation regulates gene expression by altering chromatin accessibility. These modifications impact nucleosome spacing, making DNA either more accessible for transcription or silenced. In females, one X chromosome is inactivated by such modifications, impacting gene expression by changing nucleosome packing.
Step-by-step explanation:
Activation domain modification of local chromatin structure refers to the epigenetic changes that either facilitate or restrict access to the DNA, thus controlling gene expression. These modifications include the addition or removal of chemical modifications like acetyl, methyl, or phosphate groups to DNA or histone proteins. For instance, histone acetylation typically results in a less positive charge on the histones, which in turn allows for the chromatin to adopt a more open conformation, thereby making the DNA accessible for transcription. Conversely, histone de-acetylation leads to chromatin condensation, preventing transcription. Similarly, histone methylation can either activate or repress transcription, depending on the specific amino acids modified and the number of methyl groups added.
In the context of X chromosome inactivation in females, epigenetic changes lead to one X chromosome becoming highly condensed into a silent form known as Barr Body. This condensation involves the packing of nucleosomes in such a way that gene expression from the inactivated X chromosome is largely prevented, demonstrating the integral role of chromatin structure in gene regulation.