Objective of epigenetics: Study of stable and heritable gene expression patterns (and the associated phenotype), dependent on chromatin structure and independent of changes in DNA sequence. The word epigenetics comes from the ancient Greek epi – plus, above, in addition to, exterior a– and genetic – genitive– or genesis – origin–. While genetics is the science of genes, inheritance, and diversity of living organisms based on variations in the nucleotide sequence of DNA (material basis of genes), epigenetics is the study of heritable changes in gene expression patterns - and the cellular phenotypes associated with these expression patterns - caused by mechanisms that do not involve variations in the nucleotide sequence in DNA. Examples of epigenetic mechanisms are DNA methylation and the modification of histones in nucleosomes, which can be maintained through cell divisions throughout the life of an organism and can even last for several generations. An example of an epigenetic phenomenon is the process of cell differentiation during embryonic development: from a zygote, first totipotent stem cells originate, which then differentiate into the different pluripotent cell lines of the embryo. , which in turn will become the different cells completely differentiated in the adult organism. Multiple environmental factors, such as maternal nutrition, can affect the development of the embryo and the adult organism through epigenetic mechanisms.