The study of biological mechanisms that will switch genes on and off.

• A. Epigenetics
• B. Gene Therapy
• C. Genetic testing
• D. Cloning

Answer: (A)

Gene expression is regulated by mechanisms that decide when a gene is active. Epigenetics studies those controls—chemical tags on DNA or on histone proteins and the way DNA is packaged into chromatin—that influence transcription without changing the DNA sequence. For example, DNA methylation can suppress a gene, while histone acetylation can open up chromatin to promote transcription. These changes respond to development and environment, making gene activity dynamic.

Other options describe different ideas: gene therapy aims to alter genes to treat disease, genetic testing analyzes DNA for variants, and cloning creates identical copies. None of these focus on how the cell turns genes on or off, which is why epigenetics is the best answer.