Abstract
Epigenetic variations are inherited or uninherited effects that occur beyond the DNA sequence of an individual. However, DNA sequence has a critical role in shaping epigenetic variation. The great diversity of epigenetic markers confers an advantage of various uses without interrupting its highly environmental independence. The epigenetic effects are highlighted by many vital events, especially the regulation of gene expression in hybrid vigor and inbreeding depression, even in the absence of genetic diversity. However, various stress genes can include many repeats that undergo alternately methylation and demethylation states to regulate gene expression positively or negatively. After all the arguments raised on the genetic basis of hybrid vigor in its both traditional and molecular aspects, the term “epigenome” strongly emerged as one of the main causes of performance deviation among offspring. These include both histone and DNA biochemicalmodifications, which play a key role during successive stages of development and differentiation in addition to the regulation of gene expression in response to biotic and abiotic stresses. Evidence has shown a correlation between unique DNA methylation and heterosis in many plant species as well as between inbreeding and the sharp decline in fitness of most naturally cross-pollinated species. Although detailed molecular mechanisms laying behind many of these plant breeding aspects remain little understood, epigenetics has provided some explanations.