Epigenetics
Epigenetics is the study of changes in gene expression that occur without altering the DNA sequence. Epigenetics usually involves changes that persist through cell division, and affect the regulation of gene expression. Such effects on cellular and physiological traits may result from environmental factors, or be part of normal development.
The term also refers to the mechanism behind these changes: functionally relevant alterations to the genome that do not involve mutations in the nucleotide sequence. Examples of mechanisms that produce such changes are DNA methylation and histone modification, each of which alters how genes are expressed without altering the underlying DNA sequence. Further, non-coding RNA sequences have been shown to play a key role in the regulation of gene expression. Gene expression can be controlled through the action of repressor proteins that attach to silencer regions of the DNA. These epigenetic changes may last through cell divisions for the duration of the cell's life, and may also last for multiple generations, even though they do not involve changes in the underlying DNA sequence of the organism; instead, non-genetic factors cause the organism's genes to behave (or "express themselves") differently.
The idea that heritable genetic evolution can occur without changes in the genetic code (DNA) has called for revisions or extensions of the
Modern Synthesis or Neo-Darwinism of the twentieth century.
The idea of extending the modern synthesis was called for in the 1950s by C. H. Waddington, argued for on the basis of punctuated equilibrium by Stephen Jay Gould and Niles Eldredge in the 1980s, and was reconceptualized in 2007 by Massimo Pigliucci and
Gerd B. Müller.
The
Extended Evolutionary synthesis revisits the relative importance of different factors at play, examining several assumptions of the earlier synthesis, and augmenting it with additional causative factors. It includes multilevel selection, transgenerational epigenetic inheritance, niche construction, evolvability, and several concepts from evolutionary developmental (Evo-Devo) biology.
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