You Are What Your Granddad Ate
You are more than the sequence of your genes.
No one should find that particularly controversial: there are differences between genetically identical twins, after all, and the concept of X-chromosome-inactivation (with an obligatory picture of a calico cat) was part of my high school intro bio class a quarter century ago. It also shouldn’t come as a surprise that in multicellular organisms like humans, different types of cells express different genes, even though their DNA is the same.
Diet and environment can induce some of those changes. For example, there are compounds in broccoli that can potentially prevent cancer by altering the packaging of DNA. And smoking tobacco can cause modifications of your DNA that likely increase the risk of cardiovascular disease long after you quite smoking. These changes are considered “epigenetic” rather than “genetic”, because they alter gene expression through the addition of small chemical groups to the DNA or to the proteins that bundle the DNA, rather than by altering the DNA sequence itself.
I’m sure some of you reading this are thinking that this isn’t particularly exciting. We all know that eating vegetables is good for your health and smoking is bad for your health, no matter what biochemical changes are going on inside your cells. But there’s more to it than that. What has brought epigenetics recent attention in the popular science press recent studies showing that epigenetic changes are heritable.
For example, some mice have an epigenetic modification that alters the expression of the agouti gene: adult mice that are affected are yellow-furred, obese and diabetic, while genetically identical mice are sleek, brown-furred and healthy. This epigenetic modification is inherited from the mother, and can be affected by the chemicals the mother is exposed to during pregnancy, such as the nutritional supplements folic acid and vitamin B12, and bisphenol A, a chemical used in the manufacture of plastics. And it’s not just the mother’s diet and chemical exposure during pregnancy that affects expression of agouti – epigenetic changes caused by diet can be passed on to grandchildren.
And while most of the research has focused on mice, for obvious ethical and practical reasons, data has been emerging that humans are similarly affected. For example, the detailed records of births, deaths and harvests in Sweden have been used to look at how the availability of food affects lifespan of subsequent generations. It turns out that, if a boy had lots of food available just before puberty, his grandchildren had shorter lifespans due to diabetes and cardiovascular disease than members of the same generation whose granddads had less food to eat. You are, at least in part, what your grandparents ate.
So it’s a combination of your DNA sequences and your environment and your parents’ and grandparents’ environment that has made you what you are. Insurance companies are probably already trying to figure out how they can use that information to raise people’s premiums. And while studies have primarily focused on diabetes and cardiovascular disease, it’s plausible that development of the nervous system could also be affected. Maybe those grandkids not only have a higher risk of diabetes, but are smarter too or less likely to commit suicide.
Human genetics is usually portrayed as pretty simple in science fiction. Encourage people with long-lived grandparents to have children generation after generation and a century later you’ve doubled that population’s expected life span. If parents want specific traits in their children, it’s as easy as selecting them from a menu followed by a little cutting and pasting a bit of DNA. Of course it’s not too surprising that the complexity of biology is often ignored, since, as Calvin Johnson pointed out in a post here last week, science fiction is really about our response to science and technology, rather than the technology itself.
But that means that there a lot of interesting science – like epigenetics – that hasn’t been explored in fiction. I expect that will change in the near future. Nancy Kress (who has frequently incorporated bioscience into her fiction) has noted on her blog that it’s something she plans to explore. I’m hoping more writers follow suit.
More about epigenetics:
- Nova: “Ghost in Your Genes“
- Science Now: “Epigenetics“
- Discover Magazine: “DNA Is Not Destiny“
- Genetic Science Learning Center at the University of Utah: Epigenetics
Technical reading:
(All articles below are available for free online. Note that this is not anywhere near a comprehensive list of references.)
Cooney CA. Germ cells carry the epigenetic benefits of grandmother’s diet. PNAS 103(46): 17071-17072 (2006), doi:10.1073/pnas.0608653103
Gilbert SF. Ageing and cancer as diseases of epigenesis. J. Biosci 34:601-604 (2009); doi:10.1007/s12038-009-0077-4
Morgan HD, et al. Epigenetic reprogramming in mammals. Human Molecular Genetics 14(Review Issue 1):R47-R58 (2005); doi:10.1093/hmg/ddi114
Waterland RA and Jirtle RL. Transposable Elements: Targets for Early Nutritional Effecs on Epigenetic Gene Regulation. Mol Cell Biol. 23 (15):5293-5300 (2003); doi:10.1128/MCB.23.15.5293-5300.2003
Pembrey ME. Time to take epigenetic inheritance seriously. European Journal of Human Genetics 10:669-671 (2002): doi:10/1038/sj.ejhg.5200901
Thanks for this great essay. I read a book a couple of years ago that talked some about epigenetics in reference to fat metabolism — How Fat Works by Philip A. Wood — also about other aspects of genetics in obesity, diabetes risk, etc. But some of these details — wow — makes me wonder quite a lot about the genetic risks of household cleaning products & GMO foods, psychopharmaceuticals (like antidepressants) amongst other thing.
I’m afraid the science fictiony ideas this brings to mind are mainly of the “mad scientist” variety. E.g., mad science + evil corporation (thinking Monsanto) = multigenerational epigenetic science project to create an endemic health problems that will keep the pharmaceutical arm of the corporation in business for a long time to come. But I’m sure there are beneficial aspects to epigenetics too — I’m just too paranoid to think of ‘em. (Not a big fan of genetic engineering here.)
Coincidentally, I was just listening to some audio lectures on epigenetics recently.
Your example of a boy with lots of food to eat bequeathing his descendents with diabetes is interesting, as the classic example is just the opposite: famine (during pregnancy) leading to diabetes and other metabolic disorders: http://en.wikipedia.org/wiki/Dutch_famine_of_1944#Scientific_legacy
I’m no expert, but epigenetics is related to cell differentiation and somatic development (okay, those are probably the wrong words). This has both SFnal and real-world consequences. If we could control epigenetics we’d have less need for stem cells, or rather we could turn the clock more easily, and also cloning would be easier. When Dolly the sheep was conceived, it was by taking a sledgehammer (in this case electric shock) to the epigenetics of the adult somatic cell.
Here’s some ignorant speculation, and I’m hoping Peggy and Athena can swoop in and correct me, but I think introns are related to gene switches and epigenetics, and humans have a huge number of introns; whereas bacteria have virtually none. Is the difference between “advanced” organisms not just the sheer number of genes but also more sophisticated epigenetic orchestration? If so, one could imagine a New Species of humans with virtually the same set of classic genes but with even more enhanced epigenetics…
Okay, I’m ready to be corrected now
Mel, Calvin, quick replies — we all know this topic is bottomless.
Mel, Monsanto’s biggest sin is not selling genetically modified seeds, but making them sterile so that farmers have to buy their stock each time. This has little to do with mad scientists. Antidepressants are essentially placebo medicine — which works as such, because they have severe side effects that cannot be masked. The drug companies did small, short-term studies and only published results that favored their conclusions (“Prescribe a lot!”). The latest New Yorker has a terrific article that covers the entire antidepressant issue.
Calvin, eubacteria are the only organisms lacking introns. Archaebacteria have them, eubacteria eliminated them rather than the rest acquring them. It’s true that as you go up the evolutionary ladder alternative splicing increases (not necessarily intron specific and collective length, which tends to vary randomly across species). So does the number and complexity of miRNAs. Between these two processes, plus the constant, dynamic interaction of the genomic products, you get the complexity and sophistication that you mention.
Holy conkydink Batman! I JUST discovered the crazy topic of epigenetics and here you are writing about them. Thank you for the insightful article. Really hit the high notes of what I’ve been looking at so far.
I feel like most of the research has been done on physicological epigenetics, but the most fascinating part of it for me are the psychiatric aspects of it. It could concretely provide links that show the impact our thoughts and emotions have on our physiology, even down to our DNA. Such an interesting topic
Does anyone have any more resources on it that they have found useful?
Thanks for sharing all of this. Totally feeds my newfound curiosity
You’ve really captured all the eesnsitals in this subject area, haven’t you?
I love epigenetics. It’s one of those big picture-small picture things that hopscotch across specialities, if you want to look for it. Agriculture -> nutrition -> medicine -> reproduction -> evolution, and back around again.
I fantasize that even though my son is growing up in a city, inside him, there’s still a bit of the desert I grew up in. Granted, if it were measurable, it’d probably show up like the the products of me (and the previous four generations of my family) eating an iron-rich diet, drinking a lot of whole milk, and getting an awful lot of sunshine. And, perhaps easier to detect, the results of generations of we farmhands’ exposure to pesticides and herbicides. :S
But there’s the thing. The fantasy. Epigenetics makes good hard scifi, for sure, but this is one area of science that that already works so well in fantasy. If only they would build worlds deep enough to show it, anyway.
“You’re a green-haired pixie, poor child, because your grandad foraged in the King’s orchard.”
“Next time I see him, I’m gonna spit a seed in his eye!”
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