Scientists have know for years the epigenome is affected by the environment but until recently they did not know that these changes can be passed on to offspring (p 159). As a result, Shenk claims that “lifestyle can affect heredity” (p161). This means that what you do can directly affect your offspring and future generations of you family. Also, this affects our commonly held view on evolution and supports Lamrack’s idea of evolution “in it’s most basic form” (p 161).
With this knowledge in mind, is it possible for parents to control gene expression in their offspring? Can parents, with the help of new genetic technologies, determine the lifestyle they need to have in order to produce offspring with desired genes? Provide background information on epigenomes and their effects (Chapter 18.2 & 16.3) and recent studies that refer to epigenetics.
Sid Dash
sdash27@gmail.com
The Argument
Stephen Ornes from CR Magazine has noted how “Epigenetic changes to an individual cell are heritable. This means when a cell divides, its offspring, and all succeeding generations, carries the same epigenetic alterations—even if they were DNA methylations originally caused by environmental factors like cigarette smoke or radiation” (http://www.crmagazine.org/archive/Winter2010Sidebars/Pages/AreEpigeneticChangesInherited.aspx). Although the example Ornes gives may be somewhat bleak in its outlook, the same notion can be applied to benefit the offspring. For instance, it may be highly plausible for an Olympic athlete that trains at Colorado Springs to alter his or her epigenetics in order to increase levels of erythropoietin, and then afterwards produce offspring that carry over that same epigenetic alteration that allows for more erythropoietin. So yes, parents can indeed “control” the genes of their offspring based on their own lifestyle.
ReplyDeleteBut here is the catch, and also the reason why I DO NOT believe the idea of a parent altering his or her epigenetics simply for the sake of passing it on to offspring would be a productive idea. According to Campbell, “modifications to the chromatin CAN BE REVERSED,” (358) which obviously makes sense; the primary point of Shenk’s argument is that humans are not completely bound to the genes they are born with because they have the capacity to alter their epigenetics. But the idea of epigenetics being alterable is not a one-way street: an organism with a certain epigenetic alteration has the potential to lose that change in the same way that it was gained to begin with because the alteration is dynamic and reversible.
In order for a certain epigenetic change to remain throughout generations, the cause for the epigenetic alteration must be continually reinforced. Jean-Baptiste de Lamarck founded his basis of evolution on observations of the giraffe, claiming that “From this habit [of browsing on the leaves of trees and making constant efforts to reach them] being long maintained in all its race, it has resulted that the animal’s neck is lengthened” (Shenk 156). The giraffe’s passing of epigenetics that kept providing for longer and longer necks occurred because giraffes endlessly faced the challenge of having to reach for foods at higher altitudes. Even if we focus on Darwinian evolution over Lamarck’s theory of evolution, the concept remains the same: genes or epigenetics that allow for a certain trait will only exist as long as the local environment renders that trait to be favorable. The long neck of the giraffe would cease to exist if all of a sudden giraffes found themselves confined to an environment where all the food was located near the ground.
Taking the same concept to the human level, purposeful inherited epigenetics loses much of its shine. Referring back to the example of the offspring-bearing Olympic athlete, the child would most likely lose that erythropoietin-producing epigenetic alteration if he or she does not undergo strenuous and demanding training that would make such an alteration worthwhile; in other words, the erythropoietin would not be of any advantage in the child’s low physical intensity environment. The body would find that the increased erythropoietin production is not worth the extra ATP being spent for the little amount of activity the child undergoes, and the child would consequently lose the alteration the parent worked to pass on, thereby rendering the efforts futile. But certainly, if the parent drives the child to partake immensely in the given area, then by all means the parent can go ahead to favorably
Part 1
ReplyDeleteEpigenetic inheritance has the potential to give an advantage or disadvantage to future generations. A study supported the claim “higher rates of heart disease and diabetes in the children and grandchildren of people who were malnourished in adolescence” (http://www.sciencedaily.com/releases/2009/05/090518111723.htm). The study indicates that decisions well before pregnancy impacted the next generation and occurs because environmental influences such as diet and nutrition can alter our epigenome. We cannot alter our genetic sequence, but we can alter “additional instructional material – known as epigenetic material – which helps guide how the genes will be expressed” (Shenk 118). Then the epigenetic material that was altered by the environment will passed on to future generations.
Epigenetics may mislead some to believe that Michael Jordan’s hard work will cause his children to succeed in basketball without any work on their part. However, the advantage epigenetics plays is most likely insignificant compared to the environmental factors of Jordan’s children. I agree with Mark in that the idea of epigenetic advantages being passed down only play a significant role if the future generations actually use those genes, but want to reiterate that in the GxE model, the genetics is only one of two factors; the environment is the other half that can completely alter the outcome. The environment isn’t limited to the work ethic of the next generation, but includes mentors and the literal environment where development occurs. While parents may be able to control some of the genetics passed down to their children, the parents cannot control gene expression because gene expression also depends on the environment unique to the child. Talent cannot only come from some epigenetic advantages passed down as Shenk gives the example of Ted Williams, whose extraordinary talent is not owed to “giftedness” by genes or epigenetic material, rather his talent was “the sum of what he put into the game” (Shenk 6). There are countless examples of extraordinary talented people who trained intensely to achieve greatness. Our genes, including inherited epigenetics, gives us our potential and possibly a slight advantage, but in order to unlock greatness, the environment must be taken into consideration. For example, cab drivers in London have adapted to their demands as the streets in London are very confusing and the average person can’t navigate them. According to Scientific American, “navigational demands stimulate brain development” and “that their intensive training is responsible for the growth” (http://www.scientificamerican.com/article.cfm?id=london-taxi-memory). The body can respond to demands placed on it by biochemical changes that will “trigger the activation of dormant genes within the cells’ DNA” due to the plasticity of the brain (Shenk 69). Therefore, most who we are is related to the GxE of ourselves in the present, and less on the GxE of generation before us even though epigenetic inheritance does serve an important role passing traits along generations.
- Akshay Ramachandran (ramachandran.akshay11@gmail.com)
Part 2
ReplyDeleteI agree with Mark in his statement that “the long neck of the giraffe would cease to exist if all of a sudden giraffes found themselves confined to an environment where all the food was located near the ground”, but want to point out that epigenetics doesn’t necessarily have to apply to an entire species to have an effect. If only one family of giraffe were to continually stretch their necks, then just that family would still have long necks. For instance, the Kalenjin Tribe in Kenya accounts for about 90% of the runners from Kenya (Shenk 103); all of Kenya doesn't need to “continually reinforce” the epigenetic alteration, a minimum of one offspring in consecutive generations does.
The biological theme of evolution is integral in understanding epigenetics. “Evolution is a process that results in heritable changes in a population spread over many generations” (http://www.talkorigins.org/faqs/evolution-definition.html). Many environmental and genetic factors go into changing an organism’s evolutionary make up. Over extended periods of time, a change in the nucleotide sequence of a gene may affect the function wherever the gene is expressed. Also, changes in the regulation of gene expression can be limited to a single cell type (Campbell 527). The current belief is that evolution is “a process in which new forms arise by the slight modification of existing forms” (Campbell 529). Essentially evolution is not goal oriented, but instead happens because it needs to happen over time for an organism to survive. An “evolutionary trend does not imply that there is some intrinsic drive toward a particular phenotype” (Campbell 531). Evolution is result of the interactions between organisms and their environment. Furthermore, if “environmental conditions change, an evolutionary trend may cease or even reverse itself” (Campbell 531), hence parents cannot control gene expression because they cannot necessarily control all of their children’s environment.
- Akshay Ramachandran (ramachandran.akshay11@gmail.com)