Final answer:
The incorrect mechanism for siRNA- and miRNA-based gene regulation stated in the options is DNA methylation, as siRNA and miRNA do not directly modify DNA.
Step-by-step explanation:
The incorrect mechanism involving siRNA- and miRNA-based gene regulation from the options provided is c) DNA methylation. siRNA (small interfering RNA) and miRNA (microRNA) are both involved in post-transcriptional gene regulation mechanisms that can lead to cleavage of mRNA, inhibition of translation, and recruitment of histone modifiers to regulate gene expression. However, they are not directly involved in DNA methylation, which is a separate epigenetic mechanism that affects gene expression by modifying the DNA molecule itself, typically without changing the DNA sequence.