Final answer:
The modification pattern of histone H3 most likely to lead to gene silencing is methylation without acetylation, as this leads to chromatin condensation and reduced DNA accessibility for transcription.
Step-by-step explanation:
The question pertains to the impact of histone modifications on gene expression, specifically gene silencing. Methylation and acetylation are common changes made to histone H3, known as the 'histone code.' The pattern most likely to lead to gene silencing is methylation without acetylation.
Methylation of histone H3 is associated with gene silencing, especially when lysines are methylated. This modification leads to chromatin condensation, making DNA less accessible for transcription. On the other hand, acetylation of histones is generally linked to gene activation, as it neutralizes the positive charge of histones, leading to less tightly packed DNA, and hence, increased accessibility for transcription. Therefore, the correct answer is B. Methylation of histone H3 only, as this modification, particularly without acetylation, will most probably lead to a more condensed chromatin structure and silenced genes.