Argument: Rainbow the cat was cloned in 2001 but didn't turn out to be the "carbon copy" they expected; the two cats had different colored fur, body type, and personalities (74). Identical twins also share genes. In 1979 Jim Lewis tracked down his identical brother Jim Springer after being separated when they were 4 weeks old. They found numerous similarities: same name, adopted brother named Larry, dog named Toy, smoked cigarettes, liked math, same color and model car, live in same area of Ohio (75).
Why are identical twins more similar than a cloned animal with an exact replica of the original's genes? Also, explain how there are so many similarities between the Jim twins if they were separated shortly after birth and grew up separately (refer to the GxE model of genes).
(Katie Donnowitz kdonnowitz94@aol.com)
Recent studies in genetics have discovered not only is DNA important to the traits of an organism, but epigenetic material plays a large role in the expression and regulation of genes and DNA. Just because Cc and Rainbow had the same DNA does not mean other material, like epigenetic material, copies exactly as well. Epigenetic tags are greatly affected by one’s environment, and the tags cause the DNA to align differently in the replica when an organism is cloned. This is most likely what caused the major differences between Rainbow and her clone (http://www.libraryindex.com/pages/2263/Cloning-REPRODUCTIVE-CLONING.html). Since Cc was raised in such a different environment, its epigenetics and gene expression could be much different. This supports the new GxE model, displaying how important the environment is to the expression of genes. This is also proven through a study done on the chromosomes of identical twin sets. It was seen that the placement of epigenetic tags in three-year-old twins lined up more than those in fifty-year-old twins. When younger, the twins are in a much more controlled, similar environment than when they are older and begin more separate tracks in life. (http://learn.genetics.utah.edu/content/epigenetics/twins/). More dissimilarities can come from the clone’s altered biology as well. In a U.S. News and World Report article, scientist Wray Herbert points out, “The clone's cells, for example, would have energy-processing machinery (mitochondria) that came from the egg donor, not from the nucleus donor” (http://www.usnews.com/usnews/culture/articles/970310/archive_006397_2.htm). Fertility may also be affected in the clone. Identical twins, on the other hand, are formed when the embryo splits during the first month of development in the uterus (Campbell 1014). Because they share the same genetic information and the same environment during development, they are much more likely to have similarities than clones. Most identical twins share the same environment for most of their lives as well, allowing their epigenetic tags to be altered in very similar ways, resulting in even more similarities. Jim and Jim were a special case of identical twins. They spent nine months in the womb and four weeks of early development together, which set a very similar foundation for each. Both grew up in the same region of Ohio, had an adopted brother, and had parents similar enough to give them the same name. This shows a similar environment for the development of both brothers. Because their family lives resembled each other so closely, it is not surprising their tastes in small things like beer and cigarettes were also similar. Shenk notes a few of their differences as well, “One of the Jims was married a third time. They wore their hair very differently. One was much more verbally articulate than the other...” (Shenk 83). Though beginning with the same genes, identical twins really become more similar because their genes usually interact with analogous environments. The power of the GxE model, instead of nature or nurture being dominant, is shown through clones and twins because of the similarities and differences between the organisms.
ReplyDeleteJenna Sherman (jsherm013@aol.com)
“None of us is stuck in some sort of destined body or life. We inherit-and we become.”(Shenk 83) David Shenk is telling us that we are not predestined to be really great or bad at something. A persons’ greatness develops from the environment that the person lived and grew up in. Because of this statement, one can say identical twins would be more likely to act the same as each other when comparing the personality two identical clones. Lots of people have this misconception of clones looking alike and acting exactly the same way from Hollywood movies like Star Wars: Attack of the Clones. The clones in this movie looked and acted exactly the same as the bounty hunter that they cloned. Because of this, people think that exact clones of themselves or pets will look and act like the original. What most people don’t know is that the traits of an individual are manipulated by the environment that they live in. In an experiment, scientists made a clone of a cat named Rainbow. The clone had the exact same genes as Rainbow, but the clone ended up looking and acting completely different for the original. Rainbow is quiet, calm, brown, and plump. The clone, Cc, is curious, playful, gray, and slender. These two cats had identical genes but had they ended up with completely different characteristics. The cause for this difference is due to the environments that they cats grew up in. Right from the beginning the cats developed in completely different environments. The original cat grew inside of a uterus in another cat while Cc was grown in a petri dish. These environmental differences contributed to gene activation and because the two environments were different, different genes were turned on or off. According to the scientists in the experiment, they said, “people who hope cloning will resurrect a pet will be disappointed. Environment is as important as genes in determining a cat’s personality. And as far as appearance, having the same DNA as another calico cat doesn’t always produce the same coat pattern. Cloning does not produce a physical duplicate, and it can never reproduce the behavior or personality of a cat that you want to keep around.” (http://www.safran-arts.com/42day/history/h4dec/22cccat/22cccat.html)
ReplyDeleteSegments of DNA are turned on and off all the time, which changes the genes of an organism and the organism’s traits. Currently, scientists have not figured out how genes are turned on and off in eukaryotes, but scientists have the understanding of how genes in bacteria are turned on and off. In the case of prokaryotes, they have operons that consist of a promoter, an operator, and a sequence of genes. When the operon is on, the genes are being expressed, but when the operon is turned off, the genes are no longer being expressed, thus changing the traits of that prokaryote. The operator is the on/off switch of a segment of DNA that can be turned on or off by a repressor that binds with a co-repressor. “All organisms must regulate which genes are expressed at any given time.” (Cambell 356) Organisms need to do this due to environmental changes that are impacting that organism. With the ability to regulate which genes are on and off, organisms can be more efficient with energy they use to help them survive and reproduce. In the case of Rainbow and Cc, Rainbow never left its mother’s uterus during growth. In the case of Cc, the egg that was used had to exit the uterus of the cat to insert Rainbow’s DNA into the egg. Just by taking the egg out of the cat changed the environment of the egg drastically which could have had an impact on the egg. In response to the new environment, genes were being activated and inactivated. Due to this brief difference in environment, the genes of Cc were expressed differently from Rainbow even though they have the same genetic makeup.
Because of the differences in the environment between clones and the originals, clones and the originals are very different from each other in personality and appearance. Since identical twins grow up in the same environment, if they are not separated, they are more likely to have the common characteristics than clones and their originals. In the case of the Jim twins, they were separated at birth, but grew up in very similar environments. Due to the similar environments that they grew up in, they had a lot in common. Some of the things that they had in common were probably by chance like having the same name, but other factors were due to the environment. When taking a look at the other identical twins, Otto and Ewald, there were major differences between them. Otto grew up in an environment were running was big and Ewald grew up in an environment that promoted weight lifting. Even though they were twins, they grew up in different environments which influenced their genes to make them different. Because of the similar environments that the Jim twins grew up in, contributed to them having common characteristics.
ReplyDeleteEric Duresa eduresa11@gmail.com