David Shenk quotes Michael Rutter, a developmental psychopathologist at King's College, who says that genes are "probabilistic rather than deterministic" (Shenk 107). In a GxE model, what are some ways in which interactions with the environment increase or decrease the expression of different genes? How does the amount of expression of different genes increase or decrease the likelihood of the development of certain traits?
Adele Padgett, adele.padgett@gmail.com
In the proposed GxE model, many factors can lead to the expression, or lack thereof, of genes. Genes have to be activated, or switched on, for to be expressed. A change in the environment could cause the gene to be switched on, and also the extent that it is on, or off. One example of the environment affecting the gene expression of humans is height as tested by Stanford School of Medicine researcher William Greulich(26). He compared the height of Japanese children raised in Japan and the height of Japanese children raised in the U.S.A with better food and better medical care. It turned out that as a result of the environment where the children grew up, their height difference was an average of 5 inches. To investigate further into how environment could have caused this huge difference in heights, many factors should be examined. Children in America were better nourished, so their bodies rarely had any impediments when trying to grow. When children hit puberty, their body requires lots of nutrients since it uses up a lot of energy to physically grow. Similarly, if the children in Japan were not nourished properly, their body doesn’t have the required amount of energy to transcribe and translate the genes for growth/height and keep regulating the body at the same time. In that case, the body will use the limited monomers and nutrients to keep the body at equilibrium, and use whatever nutrients are left to grow. Since 2/3 of the world’s children are significantly undernourished, it now makes sense that perhaps most children’s height gene(s) are just not getting expressed as well due to the lackluster environmental factors (http://www.ajcn.org/content/25/11/1184.full.pdf). Another important contributor to height is the amount of sicknesses and diseases a child develops while growing up. Many illnesses such as intestinal disorders, cystic fibrosis, and kidney failure are just a few illnesses that can affect absorption of nutrients (http://www.intelihealth.com/IH/ihtIH/WSIHW011/9273/35323/360788.html?d=dmtHMSContent). If their energy transfer is poor, then the genes do not get expressed as much. The children in America had “better medical care”, so they were healthier and had fewer diseases while growing up. The children in Japan might have had more illnesses, and the body has to spend energy to fight the viruses. Again, the body is using more energy to keep the body regulated instead of investing the energy in growth. Lastly, dynamic elements such as sports and daily activities also contribute to the expression of the height genes. If the child played sports growing up, they were more physically fit than someone who didn’t play sports. By running and doing cardio, their blood flow is excellent and their body is stronger. This would not only lead to better health which means fewer illnesses, but would also cause an increase in expression of the height gene(s).
ReplyDeleteThe environment may turn certain genes on or off, which could affect on the final trait expressed. Genes transform amino acids into proteins which help create cells. However, genes can be turned on and off by environmental factors. Not only can different genes be turned on and off, but some genes can produce different proteins depending on activation conditions. This creates many schisms in which the final trait can be drastically different. The theme of continuity and change is shown in humans, where many genes are turned on and off, and combined to produce a specific trait. One simple example would be eye color. While most people’s eye colors can be predicted by their parents, there are people with eye colors that are not able to be explained by the Punnitt Square. As if states in The Genius in All of Us, “two blue-eyed parents can produce children with brown eyes” (24.) This is an example of the environment decreasing the likelihood of the child getting blue eyes. An eye’s color varies based on the amount of melanin in the iris pigment
Yiran Xu, yxu135@gmail.com
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Delete(http://www.allaboutvision.com/conditions/eye-color.htm). Many environmental factors could have affected the genes that code for melanin before birth, during birth, and even after birth. Since not all genes are transcribed and translated in every cell, gene regulation could’ve stopped the translation and reading of that specific gene in many different places. The environment could’ve induced the stopping of DNA demethylation and histone acetylation, or stopped the transcription by not sending transcription factors or lipid hormones. The melanin gene might have made it all the way up to transcription, but got changed at RNA editing and splicing due to alternatively splicing. After all that, it could still have been translated wrong since we know now that one gene codes for more than one protein depending on activation conditions. Lastly, it the protein that the gene codes for could be cleaved or modified to either not function at all by forming a new tertiary structure, or turn into a protein that does something else besides make a certain amount of melanin. A simple gene can be changed in many different places all due to the outside environmental stimuli. Many European babies are born with light colored eyes, and melanocytes slowly begin to produce melanin, which changes the baby’s eye colors (http://en.wikipedia.org/wiki/Eye_color). If some environmental factor like the sun, caused melanocytes to produce less melanin, the baby’s eyes would change colors due to certain genes being less expressed. The last environmental factor that could change eye color is human emotions. Many people’s eye color changes when they are angry, because anger causes the rise of blood pressure, and a cascade of events leading to the genes that code for melanin to be expressed differently, which ultimately changes the trait.
ReplyDeleteYiran Xu, yxu135@gmail.com