The answer is transcriptional and post-transcriptional regulation. Transcriptional regulation regulates the conversion of DNA to RNA by RNA polymerase. Post-transcriptional involves the regulation at RNA level. AN example of transcriptional regulation is the use of repressors on promoter regions. Post-transcriptional involves microRNA.
Through control of their transcription. This is possible through the mechanism of the non-coding regions of DNA that are significant in epigenetic. They are involved in the methylation of particular regions of DNA to silence them through folding of the DNA regions around histones.