Answer: The correct answer for the blank is-
turning off gene expression.
Gene expression refers to the transcription and translation of gene (which is a segment of DNA, coding for certain protein) so as to form a particular protein product or polypeptide.
It primarily involves two stages that is Transcription and translation.
Gene expression can be turned off by regulating any step or stage of protein expression, which results in the stoppage of protein synthesis.
Thus, option second is the right answer.
