Epigenetic Inheritance

After Mendelian Inheritance was rediscovered in the early 1900s it was recognized that some heritable traits appeared to be caused by a different mechanism. By the middle of the century geneticists referred to this phenomenon as epigenetic inheritance. As the molecular aspects of genetic inheritance were uncovered, epigenetic inheritance referred to the inheritance of variants in gene activity (or function) that did not involve a change in the nucleotide sequence of the gene. The term did not refer to any specific mechanism, simply heritable variation that was not variation in the DNA sequence.

In recent years we have started to uncover some mechanisms by which epigenetic inheritance occurs. These are covered elsewhere under Epigenetic Mechanisms but they are generally changes in gene expression that are caused by either histone modification or DNA methylation. These modifications to the structure of chromatin (eukaryotic DNA and associated proteins) affect gene expression and are preserved during DNA replication and cell division. When they are present in the chromatin of germ cells (eggs or sperm) these modifications are heritable.

With this growing understanding of the mechanisms, epigenetics today generally refers to the mechanisms but you should keep in mind that epigenetic inheritance is a general concept and the mechanisms are the way in which the inheritance occurs.

One fairly well studied example of epigenetic inheritance is genetic imprinting. A trait that is imprinted is one in which either only the maternally or paternally inherited copy (depending upon the specific trait) is actuallyy expressed. The mechanism by which imprinting occurs is DNA methlyation. You can see this link for more details on imprinting. However, it is good to think of imprinting as a mode of epigenetic inheritance and of methylation as an epigenetic mechanism.