Epigenetics primarily studies what kind of changes?

Epigenetics focuses on heritable changes in gene expression or cellular phenotype that do not involve alterations to the underlying DNA sequence. This includes mechanisms such as DNA methylation and histone modification, which can regulate how genes are turned on or off. These changes can be influenced by various factors, including environmental conditions, and can be passed down from one generation to the next without altering the genetic code itself. This ability to modify gene function while maintaining the DNA sequence is essential for understanding development and diseases, as it illustrates how external factors can lead to significant biological effects.

In contrast, the other options pertain to different biological concepts. The first option involves actual mutations in the DNA sequence itself, which is not the focus of epigenetics. The third option refers to physical mutations in chromosomes, which relate to structural changes rather than the regulatory mechanisms studied in epigenetics. Lastly, non-heritable environmental effects on genes do not involve changes that can be passed on to subsequent generations, thus falling outside the scope of epigenetic study.