Shenk expands on the basic idea of Lamarcksim, that what
someone does in his or her life can affect future generations, and asserts that
“lifestyle can alter heredity” (161).
The fact that histone proteins, or epigenomes, can be altered due to the
environment brought about many new studies which did, in fact, conclude that
“everything we do-everything we eat or smoke-can affect our gene expression and
that of future generations” (160). If one strives to be a ‘genius’, what affect
will this have on his/her children? How does the principle of epigenetics
contribute to a new understanding of evolution and adaptation? Using the interdependence
in nature relationship between histones and DNA, how come inherited epigenetics
are just as important as genetics for future generations?
Ria Singh (riasingsing@gmail.com)
Epigenetics is a very recent discovery with many questions unanswerable right now and infinite possibilities. What is known is that “lifestyle can alter heredity” (Shenk 161). Traditional genetic inheritance consists on the sequence of DNA of an offspring reflecting the DNA sequence of his or her parents. When the female gamete is formed by meiosis, the egg cell has 23 chromosomes with alleles that the mother carries. A sperm has 23 chromosomes with alleles from the father. At fertilization, the DNA from both gametes combines to form a diploid embryo. It is traditionally thought and taught (with the idea of the Punnet square) that the sequence of DNA that results determines the gene expression and traits of the offspring. Shenk is displeased that “any high school student knows that genes are passed on unchanged form parent to child and to the next generation and the next” (157). However, however recent science is breaking the faulty idea of “unchanged genes.” In reality, the sequence of DNA is not the only thing passed from parent to child; epigenomes are passed along from generation to generation as well. Epigenetic inheritance, “inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence,” also has an effect on gene expression (Campbell 358). What makes this discovery so incredible is the implication that our epigenomes “can be altered by the environment” and “changes to the epigenome can be inherited” (Shenk 159). This means everything from the food we eat to the air we breathe can affect future generations, children that are not even conceived yet.
ReplyDeleteThere are already countless experiments that prove the effect of environment such as diet and stress of future parents on their future children and grandchildren. For example, Dr. Lars Olov Bygren performed an experiment on people of the Norrbotten County in Sweden. Norrbotten in the 18th century experienced winters of regular harvest and abundant harvest which translated into irregular nutrition of normal and gluttony of the inhabitants. Bygren found some pretty telling results: “boys who enjoyed those rare overabundant winters — kids who went from normal eating to gluttony in a single season — produced sons and grandsons who lived shorter lives” (http://www.time.com/time /magazine/article/0,9171,1952313,00.html). Even before having children, the environment, in this case nutrition, affected the kids epigenomes that they then passed on to their children later in life. Shenk also quotes the Journal of Neuroscience about an article where “a stimulating environment improved the memory of young mice with a memory-impairing genetic defect and also improved the memory of their eventual offspring” (162). It is hard to test this same effect with intelligence in humans since there are so many uncontrollable factors. However, using these and other experiments, it can be said that if one strives to be genius before they have children, they may be alter their epigenome, and their children can be smarter than they otherwise would have been. In a study done with nematode Caenorhabditis elegans, Jean-Jacques Remy reports, “olfactory imprint can be transmitted to the next generation.” He suggests imprinting at an early age can alter an organism’s epigenome and “raises the possibility that a behavioral alteration produced by an environmental change might be genetically assimilated after a limited number of generations” (http://www.cell.com/current-biology/abstract/S0960-9822(10)01003-1). If one commits oneself to training to be a genius through dedication, hard work, and motivation, he or she can change their epigenome – “we can impact our genetic legacy” (Shenk 118). In fact, when humans push themselves beyond their normal capacity, their cells experience ‘“biochemical states than will trigger the activation [of] dormant genes within the cells DNA”’ (Shenk 69).
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ReplyDeleteThese biochemical changes do not change the nucleotide sequence, but rather the interaction of the DNA strands with histones. Acetylation and methylation take place to alter genetic expression and these changes in the epigenome induced by one’s decisions will be passed on their future children and grandchildren and can have a huge effect. Therefore, if people push and train themselves to be a genius, they may induce changes in their epigenome. These changes may include the loosening of DNA around a histone protein by acetylation so RNA polymerase can attach to the now exposed TATA box promoter on the DNA sequence and mRNA can be transcribed. Thus, the mRNA will be translated in proteins and the trait will be detected of brighter intelligence. This change in the epigenome can be passed along to offspring through epigenetic inheritance and the offspring could potentially be smarter as well since the gene that otherwise wouldn’t have been expressed will be expressed.
Epigenetics calls for a rethinking of the traditional methodology of evolution. Certainly, “the concept of inherited epigenetic changes does not invalidate the theory of natural selection, but it makes it a lot more complicated” (Shenk, 161). Natural selection and evolution is typically based on a variation within a population due to sexual reproduction and/or mutation that causes the offspring to have a selective advantage or no selective advantage. An organism with a selective advantage is likely to survive better and reproduce more frequently and over time that advantageous trait becomes an adaptation the whole population has. Multiple adaptations over large amounts of time will lead to evolution. However, with epigenetics we are able to adapt and evolve in a relatively short amount of time. Humans don’t have to rely on mutations and chance for selective advantages; we can produce them on our own by changing our epigenome through the environment we more or less choose. In essence, epigenetic inheritance can speed up the process of evolution since new traits can be passed on in a single generation. This theory is becoming more acceptable as “Bygren and other scientists have now amassed historical evidence suggesting that powerful environmental conditions (near death from starvation, for instance) can somehow leave an imprint on the genetic material in eggs and sperm. These genetic imprints can short-circuit evolution and pass along new traits in a single generation” (http://www.time.com/time/magazine/ article/0,9171,1952313,00.html). Although epigenetics can theoretically lead human kind to the ability to drastically change rapidly, the reality is “almost all of us conform to established cultural norms” (Shenk 118). Therefore, it is unlikely for the entire human race to develop adaptations based on epigenetics, at least not in the near future.
Since both the nucleotide sequence and epigenomes are inherited, both will affect phenotype, even though only the genetic inheritance determines genotype. Epigenetics is responsible for “switch[ing] parts of the genome off and on at strategic times and locations” (http://learn.genetics.utah.edu/content/epigenetics/). Similar to a how a painter may have a set of colors on their palette, the painter actually decides when to use which colors and where. Both the genome and the “ epigenome - packaging that surrounds DNA” are equally important factors in determining gene expression and traits. The genes contain the instructions for the proteins themselves, but the epigenomes contain the instructions for when and which genes are to be expressed.
Lizzy Ettleson, lettleson@gmail.com