Epigenetics is the study of heritable and stable changes in gene expression that occur through alterations in the chromosome rather than in the DNA sequence.

Where do epigenetic changes occur?

Most epigenetic changes that occur in sperm and egg cells get erased when the two combine to form a fertilized egg, in a process called "reprogramming." This reprogramming allows the cells of the fetus to "start from scratch" and make their own epigenetic changes.

How do epigenetic modifications occur?

Epigenetic modifications refer to changes in the gene expression that are not caused by changes in the DNA sequences but are due to events like DNA methylations, histone modifications, miRNA expression modulation, etc.