Epigenetics studies mitotically or meiotically inherited and reversible changes that affect gene expression and genome stability, but occur without a change in the DNA sequence. At the same time, environmental factors, such as metals, persistent organic pollutants, or endocrine disorders caused by chemicals, can influence epigenetic changes. The extension of epigenetics to epigenomics, as well as genetics to genomics, consists in expanding the focus of attention from specific loci to large or complete sets of epigenetic characters that influence the phenotype of an individual. Similarly, one can move from individual individuals to many related genomes and related epigenomes that make up populations or species. The epigenome consists of labeled DNA methylation and histone modifications and is involved in the control of gene expression. The epigenome is precisely reproduced during mitosis and can be transmitted between generations.
Although the major processes in the body are determined by one’s inherited and unalterable genes, epigenetic changes are mostly reliant on the environment and can affect the rate of expression of certain genes. For instance, the study on twin brothers Scott and Mark showed that epigenetic DNA methylation could be different in people with an identical genome. The process of DNA methylation is essential in epigenetics because the latter can directly determine whether a gene will be active or silenced. Most of the epigenetic changes in somatic or vegetative tissues can affect phenotypic variability and contribute to the formation of the complexity of the inheritance of characters. Patterns of alternative gene expression in eukaryotes are based on various epigenetic mechanisms mentioned above. These epigenetic markers determine constitutive transcriptional silencing and the reversibility of such a shutdown of gene expression, due to the possibility of self-maintenance in the process of mitosis. Epigenetic inheritance involves the transfer of information not encoded in a DNA sequence from parent cells to daughter cells, and from generation to generation.