The Icing on the Genetic Cake

The “nature versus nurture” debate regarding how much of “you” is determined by genetics and by your environment is just as good as any classic argument -- coke versus pepsi, the chicken versus the egg, and Chicago-style or New York-style pizza. Classic Mendelian genetics states that all of your “physical” properties like appearance and any genetic diseases are solely caused by your genetic code, and that “acquired traits” like weight, personality, eating and drinking habits, and temperament are determined by your environment. However, before Mendelian genetics came along, there was a totally contradictory theory thought-up by Jean-Baptiste Lamarck that stated offspring could in fact inherit their parents’ “acquired traits” genetically.1
Never heard of Lamarck? Don’t worry -- after Mendelian genetic theory was accepted as scientific fact, along with evolution and the idea that the Earth is round, Lamarck’s theories were banished to the pages of dusty high-school science books. However, Lamarck’s ideas, known as Lamarckian genetics, may be experiencing a revival as more and more research on epigenetics is generated compelling evidence to support Lamarckian theory. Epigenetics -- the study of the epi-, or “top,” genome -- has skyrocketed into the biological limelight within the past decade. In order to understand epigenetics and why it’s relevant, a bit must be understood about “normal” genetics as well.
A gene is defined as a section of your DNA that codes for a specific protein, and proteins pretty much control everything in your body, and genetics is the study of those genes and their inheritance. Additionally, depending on in what area of the body a certain cell is found, different genes may or may not be used. For example, a cell in your lungs doesn’t need to use the gene that produces proteins for eye color. But since every cell in your body contains a complete set of DNA, which genes are used where must be tightly regulated. This is done with histones -- special proteins around which DNA is wrapped that control which genes are “on” or “off” in a certain cell by coiling DNA tighter or more loosely, thus exposing or hiding different genes.1
So what’s the deal with epigenetics? To break it down, epigenetics controls when, where, how, and why genes are turned “on” or “off” through the use of histones and special DNA markers called acyl and methyl groups. Basically, the epigenome is the icing on your proverbial genetic cake. When methyl groups are added to DNA in a certain area, it can cause the gene to be silenced, and when acyl groups are added to histones, the gene may be expressed.1
So, epigenetics plays a role in controlling day-to-day gene expression in your cells; however, it has been found that random epigenetic changes with negative consequences -- i.e. turning off the genes that kill tumors, thus prompting cancer -- can be the result of environmental factors like prolonged exposure to toxins, excessive drug and alcohol use, obesity, etc.4 But since those changes were caused by the environment, they shouldn’t affect anyone other than that one individual, right?
Wrong -- turns out, Lamarck was onto something. Environmental epigenetic changes have recently been found to be heritable by offspring. For example, sperm from obese men have been shown to carry epigenetic markers that cause a predisposition toward obesity in children according to a study done by the Center for Diabetes Research.2Additionally, the “Dutch famine study” showed that while children of women affected by the 1944 Dutch famine were much smaller than the average baby, their grandchildren were as well, indicating that environmental epigenetic changes have the ability to cross more than one generation.3
So the classic mantra, “do as I say, not as I do,” that you find yourself telling your kids over and over? Sometimes, they may not actually have a choice! These new findings on epigenetics underscore what we’ve all always known -- the importance of making positive, healthy lifestyle choices. However, you may not be the only one reaping the benefits.  
For the visual learners or those who wish to better understand epigenetics, here is an infographic published by Collin Wiles for Genetic Alliance in 2015 further detailing what epigenetics is and how it works:

  1. Richards, Eric J. “Inherited Epigenetic Variation and€” Revisiting Soft Inheritance.” Nature Reviews Genetics, vol. 7, no. 5, May 2006, pp. 395–401., doi:10.1038/nrg1834.
  2. “Sperm Carries Information about Dad's Weight.” EurekAlert!: The Global Source for Science News, AAAS, 3 Dec. 2015,
  3. Heijmans, B. T., et al. “Persistent Epigenetic Differences Associated with Prenatal Exposure to Famine in Humans.” Proceedings of the National Academy of Sciences, vol. 105, no. 44, 4 Nov. 2008, pp. 17046–17049., doi:10.1073/pnas.0806560105.
  4. Allegria-Torres, Jorge Alejandro, Andrea Baccarelli, and Valentina Bollati. "Epigenetics and Lifestyle." Epigenomics, vol. 3, no. 3 (August 26, 2013): 267-77. doi:10.2217/epi.11.22.