| Epigenetic |
Article Index for Epigenetic |
Information AboutEpigenetic |
| CATEGORIES ABOUT EPIGENETICS | |
| epigeneticsepigenetics | |
| genetics | |
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Specific epigenetic processes of interest include Paramutation , Bookmarking , Imprinting , Gene Silencing , X Chromosome Inactivation , Position Effect , Reprogramming , Transvection , Maternal Effect s, the progress of Carcinogenesis , many effects of Teratogen s, regulation of Histone modifications and Heterochromatin , and technical limitations affecting Parthenogenesis and Cloning . ETYMOLOGY AND DEFINITIONS The word "epigenetics" has been associated with many different definitions, and much of the confusion surrounding the use of the word "epigenetics" relates to the fact that it was originally defined to explain phenomena without knowing their molecular basis and with time became narrowly linked to certain phenomena as their molecular basis was discovered.Roloff, T.C., Nuber, U.A., 2005 Chromatin , epigenetics and stem cells. Eur J Cell Biol. 84, 123-135 Originally, the word "epigenetics" (as in " Epigenetic Landscape ") was coined by C. H. Waddington in 1942 as a Portmanteau of the words " Genetics " and " Epigenesis ".1 Epigenesis is an older word used to describe the differentiation of cells from a totipotent state in embryonic development (used in contrast to "preformationism"). At the time Waddington first used the term "epigenetics" the physical nature of genes and their role in heredity was not known. Epigenetics was Waddington's model of how genes within a multicellular organism interact with their surroundings to produce a Phenotype . Because all cells within an organism inherit the same DNA sequences, Cellular Differentiation processes crucial for epigenesis rely strongly on epigenetic rather than genetic inheritance. Robin Holliday defined epigenetics as "the study of the mechanisms of temporal and spatial control of gene activity during the development of complex organisms."Holliday, R., 1990. Mechanisms for the control of gene activity during development. Biol. Rev. Cambr. Philos. Soc. 65, 431-471 Another usage of the word "epigenetics" was employed by the psychologist Erik Erikson , who developed an "epigenetic theory of human development" which focuses on psycho-social crises. The modern usage of the word "epigenetic" is more narrow, referring to heritable traits (over rounds of cell division and sometimes transgenerationally) that do not involve changes to the underlying DNA sequence.Russo, V.E.A., Martienssen, R.A., Riggs, A.D., 1996 Epigenetic mechanisms of gene regulation. Cold Spring Harbor Laboratory Press, Plainview, NY. The Greek "epi-" prefix of the word "epigenetics" implies features that are "on top of" or "in addition to" genetics, and the current usage of the word reflects this—epigenetic traits exist on top of or in addition to the traditional molecular basis for inheritance. The similarity of the word to "genetics" has generated many parallel usages. The "epigenome" is a parallel to the word " Genome " and refers to the overall epigenetic state of a cell. The phrase " Genetic Code " has also been adapted—the " Epigenetic Code " has been used to describe the set of epigenetic features that create different phenotypes in different cells. Taken to its extreme, the "epigenetic code" could represent the total state of the cell, with the position of each molecule accounted for; more typically, the term is used in reference to systematic efforts to measure specific, relevant forms of epigenetic information such as the Histone Code or DNA Methylation patterns. MECHANISMS |
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