Which term describes heritable changes in gene expression that do not involve changes to the DNA sequence, often involving chromatin structure?

• A. Genotype
• B. Mutation
• C. Phenotype
• D. Epigenetics

Answer: (D)

Epigenetics describes heritable changes in gene expression that do not involve changes to the DNA sequence, often through chromatin modifications that alter how tightly DNA is packaged. Chemical marks such as DNA methylation and histone modifications change chromatin accessibility: when chromatin is open, genes can be active; when it’s compacted, gene expression can be silenced. These marks can be copied during cell division, helping maintain an active or repressed state across generations of cells, and in some cases even across generations in the organism. Classic examples include X-chromosome inactivation and genomic imprinting, where gene expression is regulated by these epigenetic marks rather than by changes in the underlying DNA sequence. By contrast, the underlying genotype is the DNA sequence itself, mutations are changes to that sequence, and the phenotype is the observable traits that result from genotype plus environment and regulation.