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Epigenetic Inheritance

Wikipedia Reference Information

In biology, while the subject of genetics focuses on how organisms can inherit traits by inheriting genes from their parent(s), which encode information for cell function as sequences of DNA, epigenetics is sometimes used to refer to additional methods of biological inheritance that do not directly relate to the inheritance of collections of genes, or soft inheritance. More specifically, it can refer to reversible, heritable changes in gene regulation that occur without a change in DNA sequence (genotype). These changes may be induced spontaneously, in response to environmental factors, or in response to the presence of a particular allele, even if it is absent from subsequent generations.

Epigenetics is distinct from epigenesis, which is the long-accepted description of embryonic morphogenesis as a gradual process of increasing complexity, in which organs are formed de novo (as opposed to preformationism). However, cellular differentiation processes crucial for epigenesis rely almost entirely on epigenetic rather than genetic inheritance from one cell generation to the next. If this were not so, then somatic cell cloning would be impossible, because a normal organism couldn't be recovered from a differentiated cell nucleus. Because cell differentiation is epigenetic, a somatic cell can be reprogrammed to become totipotent. (One of the few exceptions to this is the rearrangement of genes in the adaptive immune system—an organism cloned from a memory B cell would lack the ability to generate a full range of immunoglobulins because a portion of the DNA has been irreversibly—genetically—deleted from the genome. See: Development of B cells)

Epigenetics includes the study of effects that are inherited from one cell generation to the next whether these occur in embryonic morphogenesis, regeneration, normal turnover of cells, tumors, cell culture, or the replication of single celled organisms. Recently, there has been increasing interest in the idea that some forms of epigenetic inheritance may be maintained even through the production of germ cells (meiosis), and therefore may endure from one generation to the next in multicellular organisms.

Specific epigenetic processes of interest include paramutation, bookmarking, imprinting, gene silencing, X chromosome inactivation, position effect, reprogramming, transvection, maternal effects (paternal effects are rare, since much less non-genomic material is transmitted by sperm), the progress of carcinogenesis, many effects of teratogens, regulation of histone modifications and heterochromatin, and technical limitations affecting parthenogenesis and cloning.

The complete, up-to-date and editable article about Epigenetic Inheritance can be found at Wikipedia: Epigenetic Inheritance
http://en.wikipedia.org/wiki/Epigenetic_inheritance




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