Epigenetics has two closely related meanings:

• The study of the processes involved in the unfolding development of an organism. This includes phenomena such as X chromosome inactivation in mammalian females, and gene silencing within an organism.
• The study of heritable changes in gene function that occur without a change in the sequence of nuclear DNA. This includes the study of how environmental factors affecting a parent can result in changes in the way genes are expressed in the offspring.