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Monday, April 06, 2009

What Is Epigenetics?

Berger et al. (2009) attempt to define epigenetics.
"An epigenetic trait is a stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence."
Sounds good to me. Just about anything wold be better than the kitchem sink definition proposed by Eva Jablonka [Epigenetics at SEED].

The main examples are "DNA methylation, histone modifications, histone variants, and nucleosome positioning." These are chromosomal alterations that are passed on to daughter cells following cell division by mitosis or meiosis.

Although the Berger et al. don't mention it, these epigenetic signals are all reversible. I still don't find the term useful. It's far more accurate to refer to each of the individual examples by name and the field is "regulation of gene expression."

Berger, S.L., Kouzarides, T., Shiekhattar, R., and Shilatifard, A. (2009) An operational definition of epigenetics. Genes & Dev. 23:781-783. [DOI: 10.1101/gad.1787609]

[Hat Tip: Hopeful Monster]


  1. lol I gave Ali a ton of shit over this last time he was on campus-- he vowed that epigenetics would have a definition after that meeting. lol!

  2. I'm an undergraduate student, and the topic of epigenetics has come up a few times in my genetics class.

    My question is: If proteins like DNA/histone methyltransferases and the histones themselves are gene products, can we really say that epigenetic inheritance is independent of the DNA sequence? I understand the concept of the histone "code," where the acetylation and methylation of histones is conserved from generation to generation. However, I fail to see how this is independent of the DNA sequence in the strictest sense, since these processes are all reversible and since they were all basically specified by the DNA sequence to begin with (even if the original acetylation or methylation occurred several generations beforehand).

    Could someone please clear this up for me? I apologize if I've misunderstood anything, or if I'm just flat out in over my head here.

  3. One question. Identical twins are known to have identical DNA sequence, BUT they are known to have different fingerprints and some other differences. Is this a result of epigenetic or a stochastic developmental process?

  4. I tend to agree that in the strictest sense there's nothing "independent" about epigenetics, and I think the above definition accounts for that. The prefix "epi," in that case, is a misnomer. I'll side with Moran that the mechanisms should all be referred to individually under the field of gene expression.

  5. You guys are right. It is "gene expression" that should be expanded to include the kitchen sink.

    (Yeah, I'm being sarcastic),