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:

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

You can follow any responses to this entry through the RSS 2.0 feed.
You can leave a response, or trackback from your own site.