Epigenetic
Refers to mechanisms "in control" of (changing) gene expression (and interaction) primarily during development [e.g., of embryonic organism] which do not require changes in actual gene/DNA sequences, to occur.

Coined from the Greek epi= "upon" by Conrad H. Waddington in the 1940s, this term more broadly refers to all the non-classical genetic/heredity sources of a given organism's phenotype. For example:

  • as a plant embryo develops into a seedling (juvenile in the case of an animal), different genes are expressed [or silenced] in that organism. Analogous to mammal embryo development. For example, during 2002, researchers discovered that feeding small amounts of folic acid to certain pregnant inbred (yellow- colored) laboratory mice will cause their offspring to have brown-colored fur via an epigenetic change caused by DNA methylation because the folic acid donates methyl molecular groups to the mouse's chromatin; thereby silencing the applicable gene (known as agouti gene). When epigenetic change results from consumption of certain foods/compounds, it is referred to as nutritional epigenetics.
  • as a result of certain disease(s) afflicting the organism, different gene(s) within the organism's DNA are silenced [or expressed]. For example, hypoxia (e.g., resulting during tuberculosis or certain cancers) has been shown to result in epigenetic events within the bodies of relevant patients. When it results from cancer, it is referred to as cancer epigenetics.
  • as an organism (especially during its embryo stage) interacts with its environment, some of those environmental impacts (e.g., temperature) cause certain genes to be expressed (or silenced). For example, the eggs of the saltwater crocodile (Crocodylus porosus) yield a larger fraction of male offspring when those eggs are incubated [in the nest] at temperatures above 90oF (32oC) than when those eggs are incubated at temperatures below 90oF (32oC).
  • as an organism passes from juvenile stage to later life stage(s). For example, the female honeybee (Apis mellifera) "switches on"/off approximately 40 percent of her total genes as she matures from being a "nurse bee" (taking care of pupae while she is a juvenile) to being a "forager bee". During times in which the honeybee colony is in need of more forager bees (i.e., adults), the juveniles mature faster [to "forager bees"] than during normal times.

Epigenetic events include gene silencing, DNA methylation, chromatin remodeling, chromatin modification, histone modification, paramutation, nucleolar dominance, and gene imprinting.




The term "Epigenetic" also appears in the definition(s) of the following term(s):
Imprinting
  Hypoxia
  Hedgehog Signaling Pathway
  Epigenetic Variation
  Paramutation
  Nucleolar Dominance
  Epigenetic Therapy
 
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