The Argument – David Shenk touches on genetic clones and the
fact that they are “far from perfect copies of each other” yet “ever since
Dolly the sheep, the world has discussed clones” as if they were (73-74). He
goes on to reveal that the clone of cat Rainbow named Cc had a very different
appearance than Rainbow including different fur color and different physiques.
How is it possible that genetic clones have different phenotypes? What other cases like this have been documented? Please cite other twin and clone studies that demonstrate the effect of environmental influences on phenotype.
Lizzy Ettleson, lettleson@gmail.com
Genes are templates for the creation of amino acids that are then to be linked up into proteins which create the human body and its traits. More specifically, DNA provides the "recipe" in the form of nucleic acids which are then copied by the "scribe", the RNA polymerases, and sent to ribosomes, "the chefs", too make into proteins with the help of tRNA. Every human and every living species has the same nucleic acids that turn into the same 20 amino acids within them. What differentiates between species and among humans is the expression of the DNA, in other words: what to make and when to make it. For example, many organisms such as fruit flies, mice, and humans share the same genes; however, the activation and deactivation of these genes during the embryonic developmental process accounts for the distinctly visible differences between the species (Campbell 445). So it is more the expression of genes rather than the gene chemical composition that dictates phenotype. The expression of genes can be determined by environmental factors. In a common scenario, exposure to sun stimulates the production of melanin, causing darker pigmentation of the skin in humans. This situation illustrates the direct relationship between sunlight stimulation and higher levels of gene expression for the production of melanin, which is the chemical responsible for darker skin. In regards to identical twins, Otto and Ewald are identical who have drastically different physical build, one very muscular and the other very lanky (as pictured in Shenk 83). The reason is that one trained for strength athletics and the other for long distance running (Shenk 83). Although these men are identical in the DNA they possess, their physical outcomes vary greatly due to the differences in the physical demands they put on their bodies. Because Otto runs a lot he has a leaner body more suitable for running whereas Ewald has a more muscular body because he constantly lifts heavy weights. Gene expression produces the differences in protein mass.
ReplyDeleteBowen Jin, bowenjin2004@yahoo.com