Final answer:
Epigenetic regulation is the term for mechanisms that turn genes on or off by modifying the chromosomal structure and allowing or preventing access for transcription.
Step-by-step explanation:
Epigenetic regulation is the term for mechanisms that turn genes on or off. Epigenetic changes occur to the histone proteins and DNA and do not alter the nucleotide sequence. These changes can be temporary and alter the chromosomal structure to open or close it, allowing or preventing access for transcription.