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I have troubles understanding epigenetic: to me it seems like the study of environmental factors that change the expression rate of some genes. Therefore, it seems that it is the study of environment/genome interaction.

Is it a correct interpretation or is my reasoning flawed?

Thank you so much in advance!

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Epigenetics is the study of changes in gene function, from parent to offspring, that do not involve changes in the DNA sequence. (Source: Wikipedia)

In the original sense of this definition, epigenetics referred to all molecular pathways modulating the expression of a genotype into a particular phenotype. Over the following years, with the rapid growth of genetics, the meaning of the word has gradually narrowed. Epigenetics has been defined and today is generally accepted as "the study of changes in gene function that are mitotically and/or meiotically heritable and that do not entail a change in DNA sequence. (Dupont, 2009)

The term "epigenetic" has also been used in developmental psychology to describe psychological development as the result of an ongoing, bi-directional interchange between heredity and the environment. (Source: Wikipedia)

Within Psychology and Psychiatry, epigenetics covers areas of early life stress, addiction, anxiety, depression and fear conditioning.

Caspi et al. (2003) demonstrated that in a robust cohort of over one-thousand subjects assessed multiple times from preschool to adulthood, those who carried one or two copies of the short allele of the serotonin transporter promoter polymorphism exhibited higher rates of adult depression and suicidality when exposed to childhood maltreatment compared to long allele homozygotes with equal early life stress exposure.

One study suggested that traumatic experiences might produce an epigenetic signal that is capable of being passed to future generations. Mice were trained, using foot shocks, to fear a cherry blossom odour and the investigators reported that the mouse offspring had an increased aversion to this specific odour. (Dias & Ressler, 2013)

Addictions can arise from transcriptional and neuroepigenetic mechanisms. (Robison & Nestler, 2011)

There is caution to be made however, when looking at literature on epigenetics. Some literature has been found to be pseudoscientific as some authors have made unfounded claims that a person's genes and health can be manipulated by mind control. (Gorski, 2013)

Also, several criticisms were reported on the Dias & Ressler study, including the study's low statistical power as evidence of some irregularity such as bias in reporting results (Francis, 2014). The authors also did not indicate which mice were siblings, and treated all of the mice as statistically independent:

The statistical tests in the paper, both for the behavioral measurements as well as for the size of the M71 glomeruli , use as n, number of samples, the number of F1 and F2 individuals. This would be fine if the individuals were actually independent samples. However, they arise from a presumably small number of FO males. The numbers of FO males are not given in the paper. This is a major concern given that there is a lot of variability in the levels of expression of olfactory receptors in these mice that might be inheritable. As an example, for Figure 1a, the authors compared 16 F1-Ace-C57 mice with 13 F1-Home-C57 mice and find a p value of 0.043, with 27 degrees of freedom . But these 29 mice could have been originated from a very small number of FO mice. The actual n that should be used for the statistics in the whole paper are not the individual number of F1 or F2, but it should be the number of founding F0, for both groups. So the actual p values are larger than reported. Without the information about the size of the F0 populations used in each figure panel, it is hard to interpret the results. (Source: PubMed Comment by Gonzalo Otazu)

References

Caspi, A. et al. (2003). Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene. Science 301(5631), 386–389
DOI: 10.1126/science.1083968. PMID: 12869766.

Dias B. G. & Ressler, K. J. (2013). Parental olfactory experience influences behavior and neural structure in subsequent generations. Nature Neuroscience 17, 89–96
DOI: 10.1038/nn.3594

Dupont C., Armant D. R. & Brenner C. A. (2009). Epigenetics: definition, mechanisms and clinical perspective. Seminars in Reproductive Medicine 27 (5): 351–357. DOI:10.1055/s-0029-1237423 PMCID 2791696 PMID 19711245.

Francis, G. (2014). Too Much Success for Recent Groundbreaking Epigenetic Experiments. Genetics 198(2), 449–451
DOI: 10.1534/genetics.114.163998

Gorski, D. (2013). Epigenetics: It doesn’t mean what quacks think it means. Science-Based Medicine [Online]
Available at: https://sciencebasedmedicine.org/epigenetics-it-doesnt-mean-what-quacks-think-it-means

Robison, A. J. & Nestler, E. J. (2011). Transcriptional and epigenetic mechanisms of addiction. Nature Reviews Neuroscience. 12(11), 623–637.
DOI: 10.1038/nrn3111 PMCID: 3272277 PMID: 21989194

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Epigenetics is the study of how genes are expressed. The expression of a gene is influenced by a lot of things, and environment is generally the source of those things. Everything from what you eat, what you come into contact with, and what you do influences what genes are activated and silenced. So yes, you're correct in thinking that epigenetics is the study of environment/genome reaction.

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