Over the course of approximately pages 18 through 33, Shenk defines and explains why the old theory of G+E is no longer acceptable and what the newest theory, GXE exactly represents. Genes multiplied by the environment is very different than the former genes plus the environment. Shenk even compares GXE to baking a cake saying:
"A hundred cooks may start out with nearly the same ingredients but will in the end produce very different cakes" (23). Why and how did the maze rat experiment demonstrate the GXE theory and why is this significant to modern day biology? What other examples can you find that support the newest paradigm? Do you agree with the idea that "every level influenc[es] every other output" (Shenk 33) as shown in the diagram on page 33? Why or why not? (Jane Rose) How does this change or enhance our knowledge of evolution as a biological theme?
The maze rat experiment featured a 'gene rich' (smart) generation and a 'gene poor' (stupid) generation of mice, each living in three different environmental conditions: poor, standard, and stimulating. It was found that the mice universally performed better if living in a stimulating environment and worse if living in a poor environment regardless of patterns seen in familial/gene smarts. However, genes cannot entirely be discounted because the gene smart mice did slightly better than gene poor mice in all environments. Thus it seems that genes and environment are interacting: while genes passed on through the generations do have influence, current environment can influence traits and abilities that should already be covered by genes in the old paradigm of G+E thus the new paradigm arises: GxE!
ReplyDeleteThis is also demonstrated in the fact that Rainbow and Cc, the two genetically identical cats, don't even look the same, and act very differently This is backed up in turn by the experiment in which genetically identical mice were raised in supposedly identical environments and have certain differences (128-129), indicating that there is a constant interaction, not only between genes and environment, but also between all levels of organization in the body too.
Thus I do agree with Shenk on page 33 when he says that every level affects the others. There is no other way to explain how genetically identical mice in identical physical environments could be so different in some aspects. This realization makes evolution and natural selection even more randomized. Survival not only now counts on genes and survival challenges but also environment, hormones, proteins, chemicals, interactions, and a host of other factors as well. It partly explains why evolution takes so long to see concrete progress. the more random the system is, the longer it will take to generally improve as a species. Some individuals who are not particularly good survivors yet by chance survive and reproduce will always stick around.
Emily Reinherz...ereinherz@aol.com
There are many examples that show us that our intelligence and talents are controlled by more than mere genetics. The maze rat example is talking about how although a maze rat may run the same course many times; the route taken is always different. And when comparing to maze routes of maze rats with the same DNA they still ran different routes is amazing evidence. That shows that something more than just genetics is controlling the run and that must be the environment. We can see this is many twin experiments, early childhood development experiments and other animal-test experiments. In the book, Shenk had mentioned that the two cats, the original and the clone C.C., had the same exact DNA but turned out to look slightly different. The physical appearance is something before that shouldn’t be able to be altered in the old G+E model, but if the environment plays a role in the genetic phenotypes than even appearances can be affected as well.
ReplyDeleteThis completely changes our view of evolution. Before evolution was just the chance happening of mutations where the better mutations would survive in case of major shift in the habitat or to the food source or just due to the fact the mutation increases survival rate. It was all this idea of natural selection. That is why certain behavior of animals lasted because it gave them a little extra boost over their competitiors. (Chapter 54 of Campbell) However, evolution could be more than just these chance happenings and might have a lot to do with how our genes respond to the environment. With extensive research on how epigenomes work in making the genetics in identical twins different, we have seen a lot of evidence that shows that although twins are born with the same epigenomes, these epigenomes change as they get older in response to the environment. (New York Times) So evolution might be just the epigenomes changing how they respond to the environment, not just DNA mutation. Either way I completely agree with Shenk, but disagree with Emily in saying that GxE shows that evolution is more randomized. It shows us that we have more control over determining who we are and what we and our children become because of epigenetics and the influences of the environment.
http://www.nytimes.com/2005/07/05/health/05gene.html
Ellen Zhou (ellenzhou2006@gmail.com)