In footnote 16-17, Shenk quotes Meaney: “There are no
genetic factors that can be studied independently of the environment, and there
are no environmental factors that function independently of the genome” (177).
What evidence supports this interdependence in nature? Use specific examples to
back up your claim.
(Alexis Bauer, abauer9182@gmail.com)
The relationship between gene expression and the environment is dynamic. Gene expression is not simply expressing genes that are in DNA, and the environment will not affect all genes the same way. Genes are the construction plans for proteins but they are not the only things influencing protein construction. The environment is constantly activating and deactivating genes. As Shenk notes, “[the environment] does this in the form of environmental stimuli, nutrition, hormones, and other diagrams (Shenk 22). In most cases, characteristics such as eye color, skin color, and hair color and texture appear to be near Mendelian, but they can still be affected by the environment; for example, a child with two blue eyed parents will not necessarily have blue eyes. As Victor McKusick, a Johns Hopkins geneticist states, “two blue-eyed parents can produce children with brown eyes” (Shenk 24). This is because the environment the embryo was in could have influenced the expression of the gene that codes for melanin, which makes up the concentration of eye pigmentation. If the environment caused more histone acetlyation, it would lead to easier transcription of genes by transcription proteins, and more melanin would be produced which would produce a darker eye color due to more concentration of melanin in the eye. Hair and skin color function the same way. Two blonde parents can produce a child with brown hair simply by having a child with more tyrosinase, which is an enzyme that triggers the melanocytes to produce melanin in the cortex of the hair root. Albinism is a mutation of the gene that codes the melanocytes which causes a lack of pigmentation in the skin, eyes, and hair. Environmental factors coupled with random mutations can cause two normal parents to have an albino baby. If the genetic factors were studied independently of the environment, the chance of albinism would be a lot smaller than it actually is. In addition, just because an environmental factor affects a gene doesn’t mean it will all the time; that’s why environmental factors cannot be studied independently of the genome. One example would be hair type. Scientists hypothesized that humans developed straight hair when their ancestors traveled farther away from the equator. Curly hair makes it difficult for UV light to enter the body, so they developed straight hair. The difference between hair styles is the shape of the follicle. If the environment led the body to produce certain hormones, the follicle shape could change, which is why some children’s hair style changes from straight to curly. Sunlight does not change everyone’s hair style to straight, and producing a certain hormone will not guarantee a change in follicle shape; it is the complex relationship between the environment and the genes that shows a trait’s interdependence in nature.
ReplyDeletehttp://www.scientificamerican.com/article.cfm?id=killing-albinos-tanzania-albinism
http://www.bellasugar.com/What-Makes-Hair-Curly-Straight-2893006
http://en.wikipedia.org/wiki/Hair
Yiran Xu, yxu135@gmail.com