What is the study of heritable changes in gene activity that are not caused by changes in the DNA base sequences called?

The correct choice describes the field that investigates heritable changes in gene activity that do not involve alterations to the underlying DNA sequence itself. These changes can result from various mechanisms, such as DNA methylation and histone modification, which can influence how genes are turned on or off. This means that epigenetics is fundamentally concerned with the regulation of gene expression through chemical modifications.

Understanding epigenetics is crucial because it explains how environmental factors, lifestyle, and experiences can affect gene expression across generations. While related terms like epigenetic inheritance and epigenesis refer to specific aspects of this complex process, the term "epigenetics" encompasses the broader discipline that studies all heritable changes in gene activity without directly altering the genetic material. Gene expression, while relevant, focuses specifically on how genes are translated into functional products rather than the mechanisms that might modify this expression in heritable yet non-genetic ways.