Epigenetics is the notion that acquired characteristics can be passed on to future generations. In at least some cases, this has been verified, although it appears that the effect is not permanent, as genetic changes are known to be.
Epigenetics can affect
evolution when epigenetic changes are heritable.
[8] A sequestered germ line or
Weismann barrier is specific to animals, and epigenetic inheritance is more common in plants and microbes.
Eva Jablonka,
Marion J. Lamb and Étienne Danchin have argued that these effects may require enhancements to the standard conceptual framework of the
modern synthesis and have called for an
extended evolutionary synthesis.
[94][95][96] Other evolutionary biologists have incorporated epigenetic inheritance into
population genetics models and are openly skeptical, stating that epigenetic mechanisms such as DNA methylation and histone modification are genetically inherited under the control of
natural selection.
[97][98][99]
Two important ways in which epigenetic inheritance can be different from traditional genetic inheritance, with important consequences for evolution, are that rates of epimutation can be much faster than rates of mutation[100] and the epimutations are more easily reversible.[101] In plants, heritable DNA methylation mutations are 100.000 times more likely to occur compared to DNA mutations.[102] An epigenetically inherited element such as the PSI+ system can act as a "stop-gap", good enough for short-term adaptation that allows the lineage to survive for long enough for mutation and/or recombination to genetically assimilate the adaptive phenotypic change.[103] The existence of this possibility increases the evolvability of a species.
More than 100 cases of transgenerational epigenetic inheritance phenomena have been reported in a wide range of organisms, including prokaryotes, plants, and animals.[104] For instance, mourning cloak butterflies will change color through hormone changes in response to experimentation of varying temperatures.[105]
The filamentous fungus
Neurospora crassa is a prominent model system for understanding the control and function of cytosine methylation. In this organisms, DNA methylation is associated with relics of a genome defense system called RIP (repeat-induced point mutation) and silences gene expression by inhibiting transcription elongation.[106]
The yeast prion PSI is generated by a conformational change of a translation termination factor, which is then inherited by daughter cells. This can provide a survival advantage under adverse conditions. This is an example of epigenetic regulation enabling unicellular organisms to respond rapidly to environmental stress. Prions can be viewed as epigenetic agents capable of inducing a phenotypic change without modification of the genome.[107]
Direct detection of epigenetic marks in microorganisms is possible with single molecule real time sequencing, in which polymerase sensitivity allows for measuring methylation and other modifications as a DNA molecule is being sequenced.[108] Several projects have demonstrated the ability to collect genome-wide epigenetic data in bacteria.
Epigenetics - Wikipedia