Shenk uses John C. Crabbe’s experiment with genetically identical mice under almost identical conditions as proof that “there are many influences [in environment] that we can’t even detect” (128). Shenk’s reasoning is that, even when the mice’s environments were controlled for everything except location, ‘invisible’ variables, so minute they weren’t even considered, influenced the mice’s development. However, Shenk also states that “the differences were not consistent, but zigged and zagged across genetic strains and different locations” (129). Given the inconsistency of results with no particular variable identifiable as the cause, is Shenk’s conclusion that environment caused the disparity between mice reasonable? Using the information given in Genius and outside sources, evaluate the legitimacy of Shenk’s conclusion. Shenk also adds that “In Edmonton, the genetically altered mice tended to be just as active as wild mice, whereas they were more active in Portland and less active than the wild mice in Albany” (129). Can the activity levels of each group be attributed specifically to environment? Can the activity be attributed to a genetic tendency towards exercise, or may other factors be involved? How might each group’s behavior have allowed the mice to survive and reproduce? Consider animal behavior and community ecology (chapters 51 and 54 in Campbell) when formulating your response, and connect to the biological theme of evolution.
Mackenzie Levy (GinnyFan@comcast.net)
Although there was no variable identified that correlated with the results in the genetically identical mice, Shenk statement is very reasonable in my opinion. This can be supported by the importance of diversity and variability in our environments that allows a population to evolve. The undetectable differences from the "moment of conception" as Shenk stated in the Skype session, may be in fact necessary and work to benefit a species. These "invisible" variables can be in the molecular level and be undetectable to experiments run by humans. Furthermore, genetic mutations on the molecular level could be the cause of such variations in clones.
ReplyDeleteIn this article titled, "Forward and reverse genetic approaches to behavior in the mouse" discusses how scientists are able to isolate specific genes are amplify and clone a specific mutation in the DNA of the mouse (http://www.sciencemag.org/content/264/5166/1 724.abstract?sid=4b4f3b61-c826-49ff-bcca-e54e8c1854b8). By using the technique of identifying phenotype and then the gene, a more in depth analysis of how genes regulate behavior and phenotype are available. This article illustrates the advancements in understanding genes, but also now allows other scientists to pursue discovery on a molecular level and how different environments react to the specific isolated genes.
The genetic tendency towards exercise should have been a result of the change in atmosphere and environment. Outside of a controlled experiment, the genetic tendency toward exercise in mice could be due to the variation of climate throughout an environment, "organisms can avoid some stressful conditions temporarily through behaviors such as dormancy or hibernation" (1154). An interesting theory would be to compare the willingness of exercise to the sexual behavior of the mice. One could hypothesize that mice that are more active in the Portland environment would have a greater genetic tendency to sexually reproduce at higher rates than the less active mice.
Although genetically identical, mice showing different phenotypes due to a variety of interactions with the environment are important to surviving in different environmental conditions and adding diversity in a population. The theme of evolution shows that only the individuals fittest and possessing the best traits are able to survive in specific environments. The differences in a population are beneficial for a species to maintain diversity and a variety of behaviors important to surviving and reproducing in a specific environment.
(Weronika Dudkiewicz wpd1414@gmail.com)
Because they are genetically identical, each mouse, regardless of the surrounding and environment and location, would have the same genetic tendency toward exercise. To change the genetic tendency, environmental factors would need to influence the genes. Thus, it seems that Shenk is correct in assuming that “invisible [environmental] influences intervened” in the expression of genes despite the “painstakingly identical environments” set up in Crabbe’s experiment (129). Even slight environmental differences at different locations can stimulate or inhibit the secretion of a certain hormone in the mice’s bodies, such as melatonin, which would modify gene expression and directly impact activity levels. Ultimately, the “social interactions and surroundings” of the mice may be just different enough in order to affect how the genes of mice of different locations are expressed (Campbell 1129).On this regard I agree with both Shenk’s argument and Weronika’s above response that the “undetectable differences” in the mice’s environments accounted for the differences in activity level.
ReplyDeleteRelating to the theme of evolution, there is a selective advantage for each varying level of activity at different locations which would help the mice to survive and reproduce. However, I disagree with Weronika’s claim that the more physically active a mouse is, the more sexually active it would be. Mice trying to reproduce would be more likely to conserve energy strictly for courtship and reproductive processes, from which high activity levels would take away necessary energy. Instead, most animals would budget their energy and limit their physical activity, as controlling “energy expenditure…prepar[es] an organism well in advance for …energetic demands” such as reproduction (Arnold http://web.ebscohost.com/ehost/detail?vid=7&hid=105&sid=71045666-3895-44e3-ab17-f11b53a57275%40sessionmgr112&bdata=JnNpdGU9ZWhvc3QtbGl2ZQ%3d%3d#db=aph&AN=23520078). High levels of physical activity in the mice would likely indicate mice that are less likely to reproduce. Thus, the mice with lower levels of activity in all three locations seem to possess a selective advantage in being able to reproduce without wasting as much energy. In a non-laboratory setting, these mice with lower activity levels may also be less likely to encounter sources of food; however, given the setup of Crabbe’s experiment, it is unlikely that food is any more readily available to the more active mice. Thus, lower levels of activity would prove to be a more effective trait that would survive in the mice, yet their genes would still ultimately be impacted by the environment.
David Ribot (ribotdavid@gmail.com)