Rainbow the cat was cloned in 2001 to make Cc the cat. Although the cats shared the same DNA, their appearances and personalities were very different (74). What does this explain about the GxE model vs. the G+E model? If Rainbow and Cc shared the same DNA and appeared very different, why do identical twins, who also share the same DNA sequence, often appear very similar?
Ted Williams was one of the greatest baseball hitters of all time, and after he died in 2002, "his son, John Henry, became convinced that his father's particular genius could be equaled only by a perfect replica: a clone" (73). What is the flaw with John Henry's logic, and why is he wrong? Why and how would making a clone of Ted Williams' DNA create a different Ted Williams than the original?
Adele Padgett adele.padgett@gmail.com
The fact that two cats with the exact same DNA turned out differently in personality and physical characteristics, suggests that nothing seems to be predetermined by DNE. This idea parallels the GxE model that states that "Genes, proteins, and environmental signals constantly interact with one another" (Shenk 31). In contrast to the G+E model that states the environmental factors have little or a nominal effect on the characteristics uprooted through DNA. The distinction between the two DNA identical cats serves as proof that DNA as no more weight than other environmental factors. The differences of the environmental aspects between the two cats is responsible, assuming the GxE model is correct, for the obvious distinctions between the cats. Several environmental aspects such as abiotic features could have caused this difference. "Daily and annual fluctuations of abiotic factors may either blur or accentuate regional distinctions" (Campbell 1154), that is to say that abiotic factors such as sunlight, water availability, nutrient availability, and climate all of which "influences the production of proteins, which then guide the functions of cells, which form traits" (Shenk 31). Similarly, environmental signals such as behavior and emotion can cause a notable delineation between two organisms (such at the cats Rainbow and Cc) that have the exact same DNA. All the environmental signals weigh just as heavily on the creation of traits as DNA, that is why the cats turn out to be different.
ReplyDeleteThis idea relates to the biological theme of interdependence on nature. For the example with the two identical cats name Rainbow and Cc, although both the cats have the exact same DNA, their characteristics and personality are different due to the differences in nature. In other words, the nature or the environment in which the cat lives provoked the development of certain proteins in the body which changed the function of the cells, which changed the trait of the cat or organism. All this occurs due to the type of environment in which the organism lives, therefore its traits are interdependent on nature. Of course, this idea of the traits determined by nature is an example of a commensalism relationship between the organism and the biotic and abiotic factors in the environment. In other words, the change of traits benefits the organism while it causes no harm or benefit for other organisms in the specific environment (http://www.cbu.edu/~seisen/ExamplesOfCommensalism.htm).
The reason behind why many identical twins have almost the exact same characteristics is because not only is their DNA identical but the environmental factors they experience are very similar. Because of both the twins are both the same environmental signals and DNA, their traits will become fairly similar. In contrast, in the case of Ted Williams, the idea that John Henry suggests is not correct. Using the GxE model, if a clone was made of Ted Williams the clone would not be able to match the exact came attributes as Ted Williams. The reason for this is because the the clone's environment would be different to that of the original, therefore there would be different traits between the the clone and the real Ted Williams even though their DNA is identical.
Joseph Hugener (jah1112@comcast.net)
“Ever since Dolly the sheep, the world has discussed clones as though are perfect reproductions of adult beings. GxE guarantees that this isn’t so” (73). The conventional theory of G+E maintains that the environment does not impact Gene Expression below the cellular level. Under this paradigm, there is no direct interaction between genes and the environment nor proteins and the environment, only cells have the ability to interact and respond the environmental changes. What this implies is that certain traits oriented around genes, according to traditional Mendelian genetics, such as hair color or eye color cannot be influenced by the environment and are purely determined by genetic composition. The experiment featuring Rainbow and Cc challenges this notion by providing evidence that two specimens with the exact same DNA can have drastically different outcomes, seen in differences in hair color, leaving environment as the only possible explanation for this difference. These results strongly support the new GxE model which accredits the environment with a greater part in the Gene Expression process than does the G+E where certain aspects of Gene Expression such as hair color are detached from environmental influences. The new model of GxE takes into consideration the biological aspect of Gene Expression. The process of Gene Expression begins with a simple gene on a strand of DNA. The gene serves as the blueprint for production for particular proteins, and defines the possible proteins and types of cells that can be made (Campbell 314). Therefore, if the G in GxE is different, the end product will different by a multiple. On the other hand, genes are transcribed by RNA polymerase that receive chemical messages to undergo transcription. Some of these genes are only transcribed under specific scenarios in the life of an organism or under specific environmental conditions (Campbell 337). If these environmental demands, or E, of the GxE equation are varied, the resulting proteins and cells made will be varied as well. In the case of Cc and Rainbow, the environments under which they were raised were not alike and the environment differences during Cc’s early growth phase triggered different RNA transcription messages and led to the different end result in fur color. Similar effects can be seen in how variations of temperature surrounding turtle or crocodile eggs determine their sex or how yellow skinned grasshopper developed black skin for camoflauge when raised in black colored environments (30). These examples suggest a similar explanation for the differences between Cc and Rainbow.
ReplyDeleteIn the case of identical siblings which, like Cc and Rainbow, also share the same DNA but in most cases turn out very similarly, the reason for the similarity lies in the similarity of environment under which twins are raised. That is often in the same household. Growing up together, twins often do the same things and share the same stuff. This togetherness creates an environment that they both share and that stimulates their Gene Expression in very similar ways. Therefore, the end result is often very similar. In the rare case of Jim Lewis and Jim Springer, two identical twins separated at birth, their coincidental similarity after having developed into adults is in part due to genetic similarities and most likely largely due to environmental similarities despite living apart. Research based on Jim Springer and Lewis along with many other twins calculated heritability, identifying 60% of intelligence, 60% of personality, 40 to 66% of motor skills, and 21% of creativity to be based on genetics (77). This substantial amount of similarity based on DNA alone leaves the rest up to environmental factors which, in the case of Springer and Lewis, must have been similar enough for them to end up so alike. Given that only 40% of personality and intelligence rely on the similarity between environments, the case of the two Jim’s is not incredibly unlikely.
ReplyDeleteAll that being said, the amazing story of Ted Williams can be explained as: the right person born at the right time in the right place. Ted Williams grew up in an environment that inspired him to play baseball. Under such circumstances, Williams was motivated as a kid to practice for hours on end throughout the all four seasons year after year. His interest combined with his relentless work made Ted Williams the great batter known to history. From a biological stand point, Ted’s hard-work put demand on his body that stimulated RNA transcription to be turned by ribosomes into proteins that would enhance his baseball playing ability. Whether Ted’s genes were special is unknown. More likely is that his rigorous devotion to the sport allowed for some gene, that many people have to be produced in great number. Just like how the special gene, ACTN3, to produce powerful running muscles is present in 82% of Europeans (101), yet due to lack of sufficient muscular exercise to stimulate production of RNA for ACTN3 Europeans are almost unseen at the starting line for the 100 meter sprint event at the Olympics. So even if John Henry created a successful clone of Ted Williams, he would be unable to replicate the circumstances that Williams grew up under which were the main reasons for his success.
Bowen Jin (bowenjin2004@yahoo.com)
It has been almost twenty years since the birth of the first cloned mammals and in that time much has been observed about the results of cloning. As one would see in the movies or in other media venues, it was originally thought that two clones would be exact copies of each other. For example in the movie “The Other Me”, the main character Will Browning accidentally clones himself when using a contaminated toy science kit. The result is an instant fully-grown copy of Will (http://www.imdb.com/title/tt0246834/). This movie shows the common misconception that clones would just appear as fully-grown and developed copies of an already existing human, however, this is far from reality. The process of cloning is actually very intricate. Basically the process of cloning involves taking a somatic cell from the animal that is to be cloned (genetic donor) and the egg cell of another organism of the same species. The DNA from the egg cell is removed and discarded and the somatic cell is fused to the egg using electricity. Then the new egg is stimulated to divide like a normal zygote would. After about a week the blastocyst is implanted into a surrogate mother. After a full term of pregnancy, the mother gives birth to the genetic clone of the donor organism (http://www.clonesafety.org/cloning/facts/process/). Identical twins or genetic clones show the biological idea of heredity. The genes of the parent organism were passed down the to the offspring. There is a big difference between the genes one has and the expression of these genes. That is where the environment comes in in to play. Sure the genes are passes down from parent to child but differences in the environments of the children will result in different expression of the same genes. The process of cloning was used to clone Rainbow the cat and produce Cc the clone. Since these two cats are genetically identical, one might expect that these two cats would look and act exactly the same as well. But David Shenk says “[they] didn’t turn out to be much a carbon copy…the cats look very different (Rainbow sporting the typical calico colors of brown, tan, whit, and gold, while Cc was grey)…” (Shenk, 74). The differences amongst clones are striking evidence in favor of the GXE model, opposed to the G+E model. If the G+E model were accurate then we would see much more similarities between clones and even identical twins. The G+E model gives more credit in the final phenotype of an organism to genetics over environment. Since we see that genetically identical clones and twins often do not end up looking or acting exactly the same we know environment is a bigger player (http://www.genome.gov/25020028#al-9).
ReplyDeleteto be continued
Aaron Appelbaum (aaronbaron580@aol.com)
Continuation from above...
ReplyDeleteFrom the moment of fertilization of an actual egg or of a cloned egg the environment is affecting the development of the organism. Even the slightest change in environment at specific times can have a monumental effect on the outcome of the organism. Differences between Cc and Rainbow are also clearly obvious from the color of their fur. One may think that something like fur color of cats is entirely genetic but that may not be the case. According to genome.gov “The explanation for the difference [in fur] is that the color and pattern of the coats of cats cannot be attributed exclusively to genes. A biological phenomenon involving inactivation of the X chromosome in every cell of the female cat (which has two X chromosomes) determines which coat color genes are switched off and which are switched on. The distribution of X inactivation, which seems to occur randomly, determines the appearance of the cat's coat”. This distribution of X inactivation is a result of the environmental factors around the cat. Clones do not always look different. In the case of Dolly the sheep, Dolly looked like a mirror image of her mother. The factors that determine whether or not twins or clones will look exactly like one another are not entirely genetic. An unlimited number of environmental factors could and do affect the appearances of twins or clones. It is very possible for clones to look exactly alike and for identical twins to grow up and look completely different.
There has never been a human cloned for several moral reasons but many scientists still consider the possibilities. How would a human clone be able to live up to the expectations put on them by their donor and society? When Hall of Famer Ted Williams died in 2002 his son John Henry thought of the possibilities of cloning his father and recreating the greatness of Ted Williams. John’s understanding of cloning is inherently flawed, “the world has discussed clones as though they are perfect reproductions of adult beings. GXE guarantees that isn’t so” (Shenk, 73). The environment an offspring encounters have a much greater affect on the offspring than was previously thought. David Shenk also says that “even nonexperts intuitively knew it would never be possible to re-create Ted Williams quirk for quirk and swing for swing” (Shenk,73). The reason that two cloned humans could never end up exactly the same is because their experiences in life (part of ones environment) would be completely different. If a thirty-year-old man were to be cloned, the resulting baby would have thirty years of different experiences before the two could fairly be compared. This large gap in time and experiences would clearly result in great differences in appearance or personality between the clone and its donor.
Aaron Appelbaum (aaronbaron580@aol.com)
Even though Cc had the exact same nuclear DNA as Rainbow and should have been an exact copy according to the G+E model, she turned out with different-colored hair and a different physique (Shenk 74). This clearly disproves the G+E model of thinking about gene expression as half the clear-cut product of genes, and half the clear-cut product of environment, and rather supports the GxE theory that gene expression is constantly being molded by the environment. In the case of Cc and Rainbow, this is evidence of epigenetics at work. The reason for the differently colored coats of Cc and Rainbow can be attributed to X inactivation, a phenomenon that occurs in female mammals. An X chromosome in each of Cc’s somatic cells was inactivated (http://www.mun.ca/biology/scarr/Cloned_Cat.html). X inactivation occurs in female mammals because they have two X chromosomes, but rather than having double the genetic information coded for by genes on the X chromosome, for efficiency, “one X chromosome in each cell in females becomes almost completely inactivated during embryonic development” (Campbell 291). This then changes the genetic expression of the mammal: cats have two alleles for coloration, O and B. Because the “pattern of X-chromosome inactivation in different cells is essentially random… the movements of melanocytes to the skin cells are also randomly determined. Thus, even though Rainbow and cc have identical tortoiseshell genotypes, the exact phenotype of their coat patterns differs significantly, and their clonal identity is only apparent from genetic tests.” (http://www.mun.ca/biology/scarr/Cloned_Cat.html). The patterns are going to be different in each individual because, according to geneticist Mary Lyon, each individual cell randomly selects which chromosome is inactivated and becomes the Barr body, and there are millions of cells in a cat (Campbell 291). So while it is a product of environmental interactions, as Aaron said, it is also a product of pure chance. This can be a selective advantage because it produces genetic variation that could aid in survival and reproduction, because evolution occurs by certain genetic variations being better adapted to an environment than others and surviving to pass on their genes. As Bowen said, the genes provide a blueprint for RNA polymerase to transcribe for gene expression. However, when a chromosome is randomly selected to be inactivated, the gene is then modified by adding methyl groups to the nitrogenous bases of DNA nucleotides, changing the blueprint and transcription. In conclusion, Cc and Rainbow were genetically identical but epigenetically and phenotypically different. This occurred because of random X chromosome inactivation, and the factors that affect which chromosome is inactivated are random and can be influenced by the environment.
ReplyDeleteHowever, identical twins with the same genetic information turn out just that- identical (but it is important to note that they do not have identical personalities, although they may be similar). This is because identical twins form when one blastocyst collapses and splits into two, allowing two fetuses to develop from the same genetic information (http://www.usatoday.com/news/health/2007-07-03-52152171_x.htm). However, X chromosome inactivation occurs just after the blastocyst stage and around the time of implantation (http://main.uab.edu/show.asp?durki=20044). This means that X chromosome inactivation normally occurs before identical twins develop into separate entities, so they would have the same chromosomes inactivated and thus be identical still. However, sometimes X chromosome inactivation will occur before the blastocyst splits, causing the two twins to have different epigenetic expression. They may still appear identical but may have different gene expression, such as in the case of two identical female twins who ended up one with hemophilia and one without, due to early XCI (http://www.psychologytoday.com/blog/twofold/200902/why-some-identical-female-twins-are-different). In addition, it is important to remember that Cc was cloned from a mature cat, so they grew up in different environments, changing GxE interaction. On the other hand, identical twins usually grow up in the same household, surrounded by the same environments and interactions, and in the same time period, with many of the same conditions, therefore homogenizing GxE more. By the same logic, replicating Ted Williams’s genes today would not necessarily produce the same hitter that the original was. Ted Williams trained tirelessly for years from the time he was a boy to when he was getting his start in pro baseball, bringing home balls and hitting them until he was sure he could do it perfectly. “It was super discipline, not super eyesight” (Shenk 7). Indeed, it was later found that Williams’s eyesight was well within the range of normal human vision; replicating his genes would not be replicating some magical eye genes that would give the clone an edge in baseball; it would not be replicating the extraordinary training that went into making Williams one of the best hitters of all time. In addition, nearly everything about the environment today would be different: from inevitable factors, such as the fact that it is now decades later and gene-environment interactions would be completely different, to factors such as the fact that Williams would not be raised in the same household, with the same parents, around the same friends, and would not necessarily develop the same motivations that are necessary to achieving great talent. Even though the clone would be a male and not undergo X chromosome inactivation, GxE would ensure that he would be different entirely. “Genes aside, Williams had- like all of us- lived a life, made choices and mistakes, enjoyed friendships and endured hardships, collected memories. A clone would make different mistakes and collect different memories; he’d live a very different life” (Shenk 73).
ReplyDeleteVivian Wang (vivian.wang9895@gmail.com)