Epigenomes determine which aspect of biology?

• A. The exact DNA sequence
• B. The rate of mutation
• C. The expression of traits
• D. The number of chromosomes

Answer: (C)

Epigenomes regulate which genes are active in a cell by chemical marks that influence how tightly DNA is packaged and how accessible it is to the transcription machinery. This control changes when and how much of each gene is expressed, producing different traits without altering the underlying DNA sequence. Because the DNA letters themselves stay the same, epigenetic marks don’t change the exact sequence. They also don’t set how often mutations happen or how many chromosomes exist—that’s determined by the DNA sequence and cellular division processes. So the key idea is that epigenomes determine the expression of traits by modulating gene activity.