The common notion that “We cannot change our genes” is reinforced even in class (Shenk 157). Evolution is not a choice. Yet in 1999, botanist Enrico Coen discovered that changes to the epigenome can be inherited in the Peloria toadflax flower. Jean-Baptiste de Lamarck supports this discovery with his idea that "an individual's actions can alter the biological inheritance passed on to his or her children" (Shenk 155). Is Jean-Baptiste de Lamarck correct? Can our lifestyles change our own gene expression as well as that of future generations? How can Lamarck’s idea be connected to evolution or are they completely different things? Support your argument with the discoveries discussed (such as about the toadflax plant and the mice) as well as an explanation of how the epigenome affects gene expression.
Christine Zhao (c_zhao@ymail.com)
Shink brings out the idea that “lifestyle can alter heredity” (161). He brings this concept out with the study from botanist, Enrico Coen and John Innes Centre, by their discovery of two distinct toadflax plans. At first it seemed as if two genes were exactly the same, but it turns out that there was a difference in that the two flowers had a different packaging around the DNA. The DNA had a wrap and was wound around by protective packaging histones that protected the DNA and kept it compact as well as telling the genes to turn on and off. This discovery showed that environments do have an effect on the generations. The epigenome can be altered by the environment and is important for the GXE interaction (157-158). Another study, with identical mice, shows that a certain lifestyle can affect future generations. It is something as simple as food. The diet of the mice can alter the color of their original fur color as well as their oncoming generations (159). Some basic examples that can be brought to the concerns of humans are issues such as the issue of obesity. By being more active or less active it can create a varying change in the degree of insulin resistance, which can then increase the chance of heart disease and diabetes. (http://www.eurekalert.org/pub_releases/2008-06/aps-lca061808.php) and (http://dvr.sagepub.com/content/2/3/105.abstract) .
ReplyDeleteA way for the lifestyle to change heredity and the future generations can be shown by examples such as alcoholism. Someone that continually damages their body to take in the substance not only create a negative affect for their body as of that moment, but can also create a chain disturbance for their children. For pregnant mothers drinking alcohol can alter the genetic makeup of the fetus creating a higher chance of mutations and disorders once the fetus is a child. For any parents both father and mother alcoholism can be passed down where the child has a higher chance of being an alcoholic, by being more addicted to the substance. (http://alcoholism.about.com/cs/genetics/a/aa990517.htm).
The discovery of epigenome changing and carrying over several generations could lead to many trying to take advantage by changing their epigenes in order to benefit their children in the future by working harder in order to achieve success for themselves and for their legacy. There are many factors that can cause changes in the epigenome, but by knowing this, that “lifestyle can alter heredity”, It could lead healthier and better lifestyles. The basic knowledge of epigenetics and knowing that their actions can change their genes can make them more responsible for the children. Because they know that it will affect their child’s future. I think that they would work much harder so that their children could have the genes that might make them more successful as well as trying to create a better living environment. If people were aware of this, then this would give them additional incentive to stop, if not for them than for their children.
Lamarck’s idea of evolution can be connected. Epigenetics can be altered, but at the same time it is passed down, so it is a heredity trait in a way. His idea of epigenetics and alterations of the genes via substances taken in or the location can be brought back to the theme of interdependence in nature. How the parent lives and their lifestyle and what their environment demands in them can alter their genetic makeup and this can then lead to the oncoming generations to have similar genetic makeup unless they too have a different environment setup.
(Christine Park go2christine@hotmail.com)
While in some cases, lifestyle can alter the traits of current and even future generations, it is untrue that it can alter heredity. The cited cases relating to toadflax plants and identical mice (159) may be true in that they showed a change in the gene expression of that particular organism, but they cannot be used to demonstrate a change in heredity due to lifestyle (with the exception of certain lifestyle choices that lead to death making a lack of offspring). The logical fallacy here is to assume that correlation implies causation. For example, based solely on the information that children of alcoholics are more likely to become alcoholics, one might make the conjecture that alcoholism (a lifestyle) is hereditary, and thus an affinity for alcohol can be passed down through generations. This conjecture, however, is untrue. In reality, this occurs because of the environment in which kids become alcoholics via “a complex group of genetic, psychological, and environmental factors.”(http://www.medicinenet.com/alcohol_abuse _and_alcoholism/page4.htm) These children are more likely to become alcoholics not because they have inherited this trait, but because of their environment, a theory that fits well with the GxE model. This assumption is similar to assuming that firemen cause fires because they usually can be found at the same place. Thus, the riddle is not solved; what really is going on here is the presence of lurking variables. Campbell explicitly states in the textbook that “Only the genetic part of variation can have evolutionary consequences.” (469). Thus, the results of these experiments must be explained by the other part of the GxE model; the E, or environment, is to blame. For example, a bodybuilder, though he/she may have a predetermined genetic propensity for ability to gain muscle (testosterone levels affect many human traits “Testosterone levels in healthy men and the relation to behavioural and physical characteristics: facts and constructs”(a journal article)) cannot pass on his/her muscle mass solely because it is “in his/her genes” to be able to build such muscle. This human example given by Campbell on page 469 serves as a demonstration of the fact that lifestyle choices, such as to lift weights, do not always influence offspring directly. This influence, however, can arise as a result of the environment in which the offspring grows up, which in this case, would be an environment in which the role model lifts weights and may pressure the offspring to do so as well. This environment (and a genetic predisposition that wasn’t the result of a lifestyle choice, but rather many generations of genetic change) would be responsible for the child of this bodybuilder becoming a bodybuilder him/herself. The fact that lifestyle-altered phenotypes cannot be passed down generations relates to the theme of evolution. Evolution is by nature a slow process; it is a process that takes place over many centuries and millennia by natural selection and speciation. If it were really true that humans, or any other organism, could alter genes simply by changing the way they lived would result in incredibly quick evolutionary processes that would take only a handful of generations to result in significant change in a population. Given all of this information, I am led to the conclusion that Lamarck’s view is untrue, and that mutations and genetic mixing, such as what occurs in crossing over during meiosis, as well as systematic changes in environment, are responsible for changes in heredity.
DeleteEric Savin (Dallastarsfan13@gmail.com)
In response to the statement that "lifestyle can alter heredity" (161), there are many common misconceptions. To begin, the definition of epigenetics is “the study of changes in gene activity that do not involve alterations to the genetic code but still get passed down to at least one successive generation” (http://www.time.com/time/magazine/article/0,9171,1952313,00.html). So in terms of an evolutionary whole, in my opinion epiginetics will not change our view of evolution as much as add to it. Furthermore, Lamarck is correct in some respects, but incorrect in others. The effects of the environment can in fact change gene expression, or ones phenotype. This is even seen in Shenks novel because “when individuals deliberately push themselves beyond the zone of relative comfort… they [induce] an abnormal state for cells in some physiological systems…[which] trigger the activation [of] dormant genes within the cells DNA” (69). Based off, this a person could expect to see minimal changes in their gene expression, if not that of their children; however, for significant changes to be made, it would take much longer to surface. So in theory, Lamarck's hypothesis is in fact correct, and does relate to evolution quite closely, but it will not change our view of evolution. To understand why our view of evolution will remain for the most part stagnant, one must first understand what evolution is. In reality, “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 factors go into changing an organism’s evolutionary make up. Over time “a change in the nucleotide sequence of a gene may affect its function wherever the gene is expressed. In contrast, changes in the regulation of gene expression can be limited to a single cell type (Campbell 527). Currently, we hold the view 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). Instead, evolution is a 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).
ReplyDelete(continued) This, our current view, is in line with what epigenetics is.Epigenetics does not redefine evolution, but instead provide further insight into why evolution happens and how it occurs. I somewhat disagree with Eric's statement that epigenetics and environmental interactions cannot alter heredity. It was recently found that prions play a large role in why epigenetics came about. Prions, found inside cells can change shape based on environmental conditions such as temperature or the presence of chemicals. After they change shape, these proteins can collide with other prions and cause them to change shape as well. Soon after, “When the cell divides, both daughter cells will contain prions of both states, and the chain reaction can keep occurring in that new generation” (http://newswatch.nationalgeographic.com/2010/11/11/how_evolution_is_evolving/). When the prions interact with the rest of the cell, including the DNA, the different shapes of the prions can cause different proteins to be made, or different parts of the DNA to be read which triggers different phenotypes. So essentially, “some [prions] may actually become incorporated into the DNA” (http://newswatch.nationalgeographic.com/2010/11/11/how_evolution_is_evolving/) as a result of changes in diet, exercise, or lifestyle.These changes will then be passed down to the next generation. In terms of the mice experiment, the effect of environmental stimulation on gene expression can be seen in that "The diet of the mice can alter the color of their original fur color as well as their oncoming generations" (159). All in all, Lamarck essentially based his theory off of epigenetics, which we are now learning is essential to an organisms evolutionary progress.
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