Epigenetics refers to any factor that affects gene expression without changing the primary DNA sequence or genotype. Typical epigenetic signatures include alterations in DNA methylation that usually silence genes by blocking transcription factor binding site, histone modifications that change chromatin structure and the availabiLity of genes for transcription, and expression of microRNA antisense transcripts that target and mark mRNA transcripts for destruction. Epigenetic inheritance involves the transmission of patterns of genetic expression to subsequent generations without transmitting any changes to the primary DNA sequence.Silencing due to epigenetic changes such as DNA methylation is associated with a closed chromatin configuration and loss of accessibiLity of the DNA to transcription factors. Epigenetics is an area of increasing importance in human and medical genetics because epigenetic silencing of gene expression is a phenomenon that explains such widely diverse phenomena as X inactivation; genomic imprinting in well-known syndromes Like Prader-WilLi, Angelman, and Beckwith-Wiedemann; and carcinogenesis.