The key difference lies in what stage of gene expression they inhibit. Transcriptional silencing acts directly on the DNA to prevent transcription of the gene sequence into mRNA. It includes DNA methylation and histone modifications that block the gene from being accessed and transcribed. In contrast, post-transcriptional silencing allows transcription but prevents mRNA translation into protein. Mechanisms like RNAi using miRNAs/siRNAs target the mRNA for degradation or obstruct its translation after transcribing it.