The Argument—Shenk states that the functions of each cell
that lead to a person’s trait is determined by “which genes do get switched on,
and when and how often, and in what order” (32). Describe certain processes in
which genes may be switched on or off in animals. Also, how does this relate to
the early flaw in Hart and Risley’s experiment with the timing of the
intellectual tests in small children in different types of environments growing up (45)? How does the timing of the genes
being switched on and off affect gene expression, and ultimately traits? Relate
this back to Shenk’s GxE theory. How may we alter our traits by effectively timing environment stimuli to our genes? Relate this back to the Hart and Risley experiment.
(Christina Li, christinali208@gmail.com)
A change in gene expression is directly related to the transcription of a gene and how often a gene is transcribed. When DNA is in heterochromatin form it is unlikely for genes to be expressed since transcription factors are unable to access the DNA strands and form pre-mRNA. However, acetylation can occur in which a COCH3 group is added to the amino acids of histone proteins. DNA is wrapped twice around histone proteins making it unlikely for the genes on this DNA to be transcribed, but the acetylation loosens the DNA around the histones so transcription factors can attach to the promoter TATA box. The opposite effect can occur with methylation in which the DNA more tightly grips the histones so transcription is reduced. If transcription is reduced, less mRNA is produced, so the ribosomes have less to translate into proteins, and there is less gene expression. In addiction control elements determine whether genes will be expressed or not by binding to transcription factors that make the DNA strand bend and fold to facilitate the attachment of RNA polymerase.
ReplyDeleteProcesses in the body such as hormone release effect gene expression. For example, the hormone gastrin released from the stomach stimulates the production of gastric juices. The gene expression in parietal and chief cells is changed to produce more chlorine ions, hydrogen ions, and pepsinogen. This change induced by hormones could be caused the simple action of digestion after a meal. The LH hormone in women is increased once a month. Sent out from the anterior pituitary gland to a follicle of the ovary, the hormone stimulates ovulation. Therefore, the gene expression in the follicle cells was altered to induce the release of the secondary oocyte. In addition, one experiment discovered a changed in gene expression of primary human umbilical vein endothelial cells (HUVEC). The scientists “identified 52 genes with significantly altered expression under shear stress” as compared with the control (http://www.pnas.org/content/98/16/8955.short). The expression of these genes was measured using a microarray in which dyed transcribed mRNAs from the endothelial cells were matched to probes to distinguish which genes were being expressed.
The ability of cells to alter gene expression relates to the flaw in Hart and Risley’s pointed out in America’s Head Start Program. Many were perplexed at the programs mere “small to moderate positive impacts on three-and four-year-old children in the areas of literacy and vocabulary, and no impact at all on math skills” (Shenk 45). The problem was found to come from the children’s environment well before they began the Head Start program. Betty Hart and Todd Risley developed an experiment in which they “sampled the actual number of words spoken to young children from forty-two families at three different socioeconomic levels: (1) welfare homes, (2) working-class homes, (3) professional’s homes” (Shenk 45). The results were astounding with differences about 32 million words in four years. The more words children were exposed to, often the better readers they were. This shouldn’t be surprising since people “grow smarter if the environment demands it” (Shenk 44). Speaking to children changes the expression of genes in their brain to adapt to a more scholarly environment possible by inducing mitosis more often or affecting the production of certain proteins.
Gene expression is the effect of which genes are turned on and which are turn off. The timing of genetic expression is critical for our survival. For example, during our embryonic development, certain genes are expressed once and then never again that function because they have no other use besides embryonic development. What makes our cells different from one another is what genes are expressed. For example, “Genes are turned on and off in different patterns during development to make a brain cell look and act different from a liver cell or a muscle cell” (http://ghr.nlm.nih.gov/handbook /howgeneswork/geneonoff). The environment comes into play here with Shenk’s GXE model too since the changes in the environment could induce changes in genetic expression as a form of adaption. It is important “when and where genes are expressed, because even genes that carry no unfavorable mutations, may be rendered useless or harmful if they are expressed at the wrong time or in the wrong place” (http://www. bionews.org.uk/page_52048.asp). This change in gene expression will ultimately be seen as a change in trait or a new trait since mRNAs transcribed from the expressed genes will be coded into proteins using codons of the mRNAs that are read by ribosomes in the cell. Proteins then have the ability to display the trait.
ReplyDeleteSince gene expression is decided based upon a GXE model, the only factor humans have control over is environment. The genetic portion is already decided for us, but we have the capability to drastically alter our traits through the environment we expose ourselves to. Although this is not our decision, the environment in which the egg is fertilized, in vivo or in vitro can have an effect on “embryo gene expression and quality” (http://www.theriojournal.com/article/S0093-691X(05)00428-0/abstract). A cultured environment could and often does affect gene expression differently than internal fertilization does. Therefore, many fertilized eggs could fail to develop into blastocysts. Timing and environment can also affect our gene expression as seen with the Hart and Risley experiments. Although our brains continue to develop until much later in our lives, our early childhood years is a prime time for trait development based on our environment. Children whose environment lacked a diversity of words suffered in an “intellectual rut” (Shenk 45). On the other hand, students whose environment consisted or many words and a diversity of words, had developed the traits of better readers since their gene expression to do so at an early age.
Lizzy Ettleson, lettleson@gmail.com