Epigenetic modifications can affect the long-term gene expression without any change in nucleotide sequence of the DNA. Epigenetic processes intervene in the cell differentiation, chromatin structure, and activity of genes since the embryonic period. However, disorders in genes’ epigenetic pattern can affect the mechanisms such as cell division, apoptosis, and response to the environmental stimuli which may lead to the incidence of different diseases and cancers. Since epigenetic changes may return to their natural state, they could be used as important targets in the treatment of cancer and similar malignancies. The aim of this review is to assess the epigenetic changes in normal and cancerous cells, the causative factors, and epigenetic therapies and treatments. 1. Introduction All somatic cells possess the same genotype, since they have originated from the growth and division of a common progenitor cell. However, during the differentiation process cells become specialized and obtain a variety of functions and features by expressing and suppressing different sets of genes. Normally these settings are controlled by epigenetic processes. The genetics of changes and cell division is heritable. Epigenetic features are changed during the tumor induction and cancer development with different patterns and characteristics [1]. 2. Background The term epigenetics is made of two parts: Greek prefix “epi” which means upon or over and “Genetics” which is the science of genes, heredity, and variations in living organisms. It defines what is occurring in the physical state of the genes and chromatin. This word was first defined by Conrad Hal Waddington as the interaction between genes and their environment that creates the phenotype emphasizing that epigenetic mechanisms are different in response to a given environment. Waddington later pointed out that one of the main characteristics of epigenetic changes will occur in gene expression without any mutations. The nongenetic manifestation of traits in morphology had been introduced by Lamarck many years before Waddington propounded this idea. In this new definition, epigenetics is referred to as those changes in the genes functions which are transmitted through both mitosis and meiosis without causing any alterations in the DNA sequence [2]. 3. Epigenetic Mechanisms Epigenetic regulations are derived from the fact that the DNA packaging in the nucleus affects the genes expression directly [3]. In general, the increased condensation of DNA enhances the probability of genes silencing. In return, decreasing compression
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