Chimera (genetics)
From Wikipedia, the free encyclopedia
This article is about a type of hybrid animal.
Typically seen in zoology (but also discovered to a rare extent in human beings), a chimera is an animal that has two or more different populations of genetically distinct cells that originated in different zygotes; if the different cells emerged from the same zygote, it is called a mosaicism. Chimerism in human beings has very few (about 40) reported cases[citation needed].
Chimeras are formed from four parent cells (two fertilized eggs or early embryos fuse together) or from three parent cells (a fertilized egg is fused with an unfertilized egg or a fertilized egg is fused with an extra sperm). Each population of cells keeps its own character and the resulting animal is a mixture of tissues. An analogy is two jigsaw puzzles cut using an identical cutter, but with different pictures. A single puzzle can be made out of the mis-matched parts, but the completed puzzle will show parts of both pictures.
This condition is either inherited, or it is acquired through the infusion of allogeneic hematopoietic cells during transplantation or transfusion. In nonidentical twins, chimerism occurs by means of blood-vessel anastomoses. The likelihood of a child being a chimera is increased if the child is created via in vitro fertilization. Chimeras can often breed, but the fertility and type of offspring depends on which cell line gave rise to the ovaries or testes; intersexuality and hermaphroditism may result if one set of cells is genetically female and another genetically male.
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Concerns About Chimera Research
This is an excerpt from an article on Chimeras at the Center for Bioethics at the University of Minnesota. Their website is located at: http://www.ahc.umn.edu/bioethics/
While not completely opposed to the research, some experts and interested members of the public raise concerns about techniques and possible outcomes if initial problems are ignored. Their major concerns are the following:
Could chimeras have human brains?
If a chimera's brain is comprised of mostly human neurons with an appropriate structure, experts are questioning whether a human brain—and mind—could develop within an animal or human-animal body. The National Academies Guidelines for Human Embryonic Stem Cell Research cautions that experiments in which there is a possibility that human cells could contribute in a "major organized way" to the brain of an animal require strong scientific justification.
Projects such as the following give rise to questions regarding chimeras with human brains:
* Researchers at Stanford University are injecting human neural stem cells into mouse fetuses to study development of neurologic diseases (see project description in Definition section, above). Initial results were mice with brains that were about 1% human, but researchers could increase that percentage to 100% human brains in the laboratory mice. They anticipate that the structures of the brain, and certainly the size, would still be mouse-like even though the neurons of the brain would be 100% human. Responding to concerns that the experiment could result in brains that were more human than mouse, Stanford University's ethics committee has approved the research on the condition that if the mice developed indicators of human intelligence, such as improved memory or problem-solving, it would be time to stop the project.
* At St. Kitts Biomedical Foundation in the Caribbean, scientists are transplanting immature human brain cells into the brains of vervet monkeys, generating a human-monkey chimera.xxi This kind of research could create human-primate chimeras, with human brain cells.
An expert panel was convened by John Hopkins University in 2005 to study the potential for just such human-primate experiments to significantly change the cognitive and emotional capacities of primates—in effect, to humanize them.
The Working Group on Interspecific Chimeric Brains consisted of primatologists and other scientists, ethicists, and lawyers. They concluded that any shift in brain capacities toward the human end of the spectrum would be more likely to occur if human brain cells were introduced early in the development of the brains of great apes. Experiments in which small numbers of human cells were grafted into healthy adult brains of the most distantly related monkey species were the least likely to raise concerns.
What is the potential for humanized chimeras?
If human embryonic stem cells were to be injected into an animal embryo very early in its development, the human cells might spread through every organ system in the animal embryo. Conversely, animal embryonic stem cells could do the same thing when introduced into an early-stage human embryo. The results of such techniques could be a humanized animal (or animalized human), with physical features and behaviors that are distinctly human.
Considering this possible outcome, the National Academies' Guidelines for Human Embryonic Stem Cell Research say that no animal embryonic stem cells should be transplanted into a human blastocyst (early embryo). In addition, approval by an Embryonic Stem Cell Research Oversight committee should be secured before any human embryonic stem cells are put into an animal.
Could chimeras mate and produce human offspring?
If a female chimera with human ova (egg cells) mated with a male chimera with human sperm cells, scientists believe that it would be possible for a human fetus to be the result. Potentially, a chimera could give birth to a human. To address this issue, the National Academies Guidelines for Human Embryonic Stem Cell Research states: “No animal into which human embryonic stem cells have been introduced at any stage of development should be allowed to breed.”
How will human-primate chimeras be treated?
While already being used a t St. Kitts Biomedical Foundation (mentioned above), primates are likely to be the animal of choice in some human-animal chimera projects because of their close genetic similarities (especially in chimpanzees) to humans. While the guidelines state that “no human embryonic stem cells should be put into nonhuman primate blastocysts [early embryos],” they do not exclude chimera research at a later stage of development. While some oppose this research outright, others are assuming that human-primate chimeras will become more widespread in research and question whether they will be treated as humans or animals.
A.M. Chakrabarty, of the University of Illinois College of Medicine, asks:
"What is a human? This is not a question of the moral dilemma to define a human but is a legal requirement as to how much human material a chimpanzee must have before it is declared a part human and therefore falls under the protection of the Thirteenth Amendment….We must move beyond moral and philosophical discussions of hybrid human-nonhuman animals and be prepared to tackle the difficult legal questions that will attend not-so-distant attempts at creating such hybrids say for organ harvesting, for use as a subhuman species to perform hard manual labors, or simply for curiosity’s sake.”
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From the Center of Bioethics at the University of Minnesota:
Because human-animal chimeras contain human cells—or even tissues or organs that are primarily human—ethical concerns surround the question of just what or who chimeras are. Because they were created under laboratory conditions for research purposes, are chimeras lab animals? Or, will chimeras eventually be developed that are too human to be considered otherwise?
http://www.ahc.umn.edu/img/assets/25857/chimeras.pdf
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Your assignment is to respond to this prompt in an 11 sentence paragraph format. Publish your response as a comment to this post. When stating your opinion, consider the bio-ethic positions of both the Republican and Democratic ideologies on medically related issues such as stem cell research, right-to-life / abortion policy, human cloning, organ transplants etc.
“Should United States scientists have governmental support through tax dollars and facilities to pursue research on chimeras for use in organ transplants, neurological interventions or other possible applications to medicine? If yes, what guidelines or restrictions would you impose? If no, why not?"
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Questions? Ask in class or email me at doug@dougabshire.com. This assignment is by the end of this week. Thanks, Mr.A
10 comments:
Given the advances hybrids can bring, I truly dont believe that there is any threat towards hybrids. I could understand the ethical issues towards this, but these hybrids have the potential to harbor human body parts which can be used for human transplants. If you arent of any certain religion, this shouldnt be a problem, the only thing that that can be said negatively towards this topic is that you are being "inhumane" to these animals, which I dont see how that is possible. In-vitro fertilization is definately included in this topic, which is also another ethical controversy. In my opinion, I believe that we should put more research into the creation of hybrids, considering there are few ethicall issuses towards it.
Matt Hagen
I think that the United States scientists should have governmental support through tax dollars and facilities to pursue research on chimeras for use in organ transplants, neurological interventions or other possible applications to medicine. Even though there is a lot of ethical issues surrounding the this particular topic I believe that the government from the United States should allow and support further research on chimeras. There are a lot of positive outcomes to gain if there is further research on chimeras. We could use them to provide organs for organ transplants. Then, we could pretty much provide sufficient organs for all of the people who need them. We could use the research of chimeras for neurological interventions that will help get more detailed information about the brain and its systems. This could help to discover the source of diseases, mental illnesses, and pretty much anything to do with our neurons. The further research of chimeras could help to do so much for man kind. It will help to understand our nervous systems better and will provide an alternative source for transplant organs. In conclusion, I think that the U. S. government should provide funding for the further research of chimeras.
I think that the government should give their suppoert throught tax dollars to forward the research on chimeras for use in organ transplants, neurological interventions or other medicine treatments. I completely understand the religion based issues towards this, but these hybrids have the potential to harbor human body parts which can be used for human transplants. By doing this we would have a waiting list for organ transplants. I think that the government should put all the support as possible into chimeras and the creation of hybrids.
The appropriation of tax dollars is a very controversial topic. Bipartisan politics often influences this choice. The United States has recently had a political revolution, which will cause a change in what money is used for. As for tax dollars being spent on experimental science, I think this is a quality that America has always had. The tradition of American innovation should not be stopped. Putting more money towards hybrid research may not be the best way (because the money would have to be taken from some other program), but there should not be a factor stalling this growth. Tax dollars should not be used for this growth, however. It is not every American's ambition to produce new species, so their tax dollars should not go towards this research. Different forms of federal income can be used to finance hybrid research.
I think that if we can make hybrids to carry human organs then we should. By doing this many peoples lives can be saved. Also, you can circumvent many lethal conditions such as cancer, heart attacks, and kidney failure. In my opinion, the government should support the research into chimaerism and it's potential benefits.
I believe the government should fund chimaera research. Chimaeras can carry and be harvested for organs that can save many lives. Yes, this is slightly unfair to the animals but in arguing this moral issue is it also wrong to raise cows to eat them. It is just as necessary to eat for some as is it is to have a new heart for others. In the social contract for a society the governed require the governing to protect their rights to life, liberty, and property. I believe that if the government doesn't put money into research about chimaeras they may be costing many lives and therefore breaking that contract. However i believe that until it is proven that these animals can prodce these organs it would be a waste to mass produce them. Therefore i believe there should be much scrutiny about the testing and the results. This is a very sensitive subject but i believe that it has benefits that far outweigh the moral quams that surround it.
I have to agree with Seth on this one. Research into chimeras and the associated implications should be funded by the government. Huge amounts of tax dollars should not be allocated to it, but some funding should be set aside for the research. I am aware of the ethical/moral issues that are entwined in chimeras and the creation of mixed-genetics creatures. But like Seth said, you can't get too squirmy about raising animals to be organ donors when we raise these same animals all the time for the sole purpose of consumption. Only slightly hypocritical...Anyways, I certainly believe that the research and development in chimeras should be heavily regulated. All efforts should be void of an attempt at eugenics. No super-creatures, please. The argument of these chimeras become 'too human' is well founded, but can be watched. I believe that if you want to get technical about it all, a sheep with human kidneys is not really human. It's a sheep with human kidneys. Now, if this same sheep had more human parts than sheep parts, then I can understand that as a breach of the species' boundaries. But in all reality, this research could save hundreds, even thousands of lives on a regular basis. There are never enough organs going around.
I dont think that making hybrids is such a wrong thing to do, it's not hurting the animals. I also am biased about the hybrid situation because if you think in a religious aspect, someone might say that recreating something is wrong we should leave that up to 'God.' This subject brings up lost of cultural issue.
I dont think that the United States should give support to these procedures through tax dollars and facilities because that is making the people pay for more than what they need to. Especially if the United States recession and workers are alredy getting laid off so they clearly cannot be able to pay for anymore than what they already do. If the U.S. were to have these facilites and tax dollars then the payers will become angry with the government for making them pay for something they may need use or need.
Stephan Lopez
I think the government should not use tax money to support chimera’s research. First of all I think that in a way it’s not right to mix two species to produce other organs, these animals won’t have a normal lifestyle because they won’t be able to reproduce. Animals are not the only alternative to find information for research there are other sources that are not as controversial. I think animals should be respected. I really do believe there are other alternatives and I wouldn’t want my tax money to go to a cause that I don’t support maybe people can be saved but I just don’t think its right.
I believe that the United States scientists should have governmental support through tax dollars and facilities to pursue research on chimeras for use in organ transplants, neurological interventions or other possible applications to medicine. If there is a possibility to get organs that are transferrable to humans, we should do everything we can to further this kind of research. If we find a way to transfer organs from chimeras to humans, many lives could be saved. People with heart diseases would be able to go to their doctors and just ask them to get a sheep or some other kind of animal out and give them a heart. For the issue of whether a chimera is a human, a chimera is not a human. Though it may have human parts, it is not a human unless it can breed with a human. Another reason they are not humans, is because most of the animals won’t be able to walk up-right and they probably won’t even have opposable thumbs. Since they will have human parts, we could use them to solve many medical mysteries that befuddle us. We can test out medicines on them to solve some medical diseases. Scientists could also use some parts to experiment with or other medical uses. In conclusion, scientists should have governmental support to pursue research on chimeras for possible applications to medicine.
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