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Member Login Forgot your password?A chimera is an individual composed of cells with different embryonic origins. The debate about chimeras has focused on five main arguments.
The Unnaturalness Argument explores the ethics of violating natural species boundaries. The Moral Confusion Argument alleges that the existence of entities that cannot be definitively classified as either human or non-human will cause moral confusion that will undermine valuable social and cultural practices. The Borderline-Personhood Argument focuses on great apes and concludes that their borderline-personhood confers a high enough degree of moral status to make most, if not all, chimeric research on them impermissible.
These arguments provide different rationales for evaluating chimeric research and consequently differ in their implications both for the range of chimeric research that is unethical as well as the way chimeric research should be addressed in public policy. In classical Greek and Egyptian myth, chimeras are depicted as having parts with the morphological characteristics typical of different species.
The chimera of Greek mythology, for example, has the head of a lion, the body of a goat, and the tail of a serpent. Not all chimeras are mythical, however. In fact, each one of us is most likely a chimera, according to the modern scientific definition of a chimera as a single organism composed of cells with different embryonic origins Nagy and Rossant As we interact with other organisms over the years, their cells become incorporated into our bodies, not only through a process of consumption and digestion, but also through processes that leave the cells intact.
For example, pregnant women acquire cells from their fetuses and mosquitoes transfer blood between their successive victims. More exotic natural chimeras occur when early-stage human embryos fuse in utero, resulting in a child with two distinct genotypes. Laboratory-created chimeras include the geep, an intraspecies chimera made by fusing a sheep embryo with a goat embryo or by transplanting cells from one embryo into another Fehilly, Willadsen, and Tucker ; Polzin et al.
Like the chimeras of myth, the geep exhibits morphological traits of multiple species, with wool on some parts of its body and hair on others. The modified embryos are then implanted into surrogate mice and brought to term. If the gametes sperm or eggs of the resulting chimeric mice are descendants of the genetically engineered cells, they can then be bred with each other to produce nonchimeric offspring carrying the genetic alteration in all of their cells.
The early discussion of ethical issues raised by chimeras occurred under the heading of xenotransplantation, the use of non-human animals as a source of cells, tissues, or organs for transplantation into humans Institute of Medicine The moral argument in favor of xenotransplantation was one of beneficence: the shortage of human organs available for transplant and the inadequacy of alternatives meant that if non-human animals could serve as a source of organs, hundreds of thousands of human lives could be saved or improved each year ibid.
The main ethical problems included the health risks for the transplant recipient e. Pluripotent cells are capable of turning into any kind of tissue, and stem cells are capable of renewing themselves indefinitely. So hPSCs theoretically provide an indefinitely renewable source of any kind of human tissue, thus offering tremendous potential for basic research, drug development, and regenerative medicine NIH5— These were established by James Thomson and colleagues at the University of Wisconsin, Madison, in Thomson et al.
For example:. The gold standard for ascertaining whether non-human cells are pluripotent involves injecting them into blastocyst-stage embryos. The resulting chimeras are then bred and the offspring examined to see if all of their cells are progeny of the inserted cells.
If so, then the inserted cells were pluripotent, as evidenced by the fact that they could give rise to germ cells and, consequently, to an entire individual.In animals, this means an individual derived from two or more zygoteswhich can include possessing blood cells of different blood typessubtle variations in form phenotype and, if the zygotes were of differing sexes, then even the possession of both female and male sex organs  this is just one of many different phenomena that may result in intersexuality.
Animal chimeras are produced by the merger of multiple fertilized eggs. In plant chimeras, however, the distinct types of tissue may originate from the same zygoteand the difference is often due to mutation during ordinary cell division.
Normally, genetic chimerism is not visible on casual inspection; however, it has been detected in the course of proving parentage. Another way that chimerism can occur in animals is by organ transplantation, giving one individual tissues that developed from a different genome. For example, transplantation of bone marrow often determines the recipient's ensuing blood type.
An animal chimera is a single organism that is composed of two or more different populations of genetically distinct cells that originated from different zygotes involved in sexual reproduction.
If the different cells have emerged from the same zygote, the organism is called a mosaic.
Chimeras are formed from at least four parent cells two fertilised eggs or early embryos fused together. Each population of cells keeps its own character and the resulting organism is a mixture of tissues. Cases of human chimerism have been documented. 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 offspring being a chimera is increased if it is created via in vitro fertilisation. Tetragametic chimerism is a form of congenital chimerism.
This condition occurs through the fertilisation of two separate ova by two sperm, followed by aggregation of the two at the blastocyst or zygote stages. This results in the development of an organism with intermingled cell lines. Put another way, the chimera is formed from the merging of two nonidentical twins a similar merging presumably occurs with identical twins, but as their genotypes are not significantly distinct, the resulting individual would not be considered a chimera.
As such, they can be male, female, or have mixed intersex characteristics. As the organism develops, it can come to possess organs that have different sets of chromosomes.
For example, the chimera may have a liver composed of cells with one set of chromosomes and have a kidney composed of cells with a second set of chromosomes. This has occurred in humans, and at one time was thought to be extremely rare. Although more recent evidence suggests that this is not the case.
This is particularly true for the marmoset. Recent research shows most marmosets are chimeras, sharing DNA with their fraternal twins.September 17, report. In their paper published in the journal Nature ChemistrySubhendu Bhowmik and Ramanarayanan Krishnamurthy outline their theory and argue that it makes more sense than the traditional explanation for how life got its start on Earth. For many years, the consensus among scientists looking to understand the origins of life has been that a pre-RNA precursor with building blocks arose in the prebiotic soup.
One major stumbling block to proving that such a scenario led to the development of life has been the inability to explain how RNA could replicate itself in a sustainable way. Bhowmik and Krishnamurthy disagreed, suggesting instead that the weaker hybrid molecules would make it easier for nature to transition to pure RNA and DNA. This meant the molecules were not subject to the replication problem with pure RNA.
They acknowledge that no known living creature has any sort of chimeric RNA-DNA in its genome—but they also point out that other researchers have been able to force it into an E.
And some other microorganisms make them seemingly by accident—but then very quickly eliminate them. Explore further. More from Chemistry. Your feedback will go directly to Science X editors. Thank you for taking your time to send in your valued opinion to Science X editors. You can be assured our editors closely monitor every feedback sent and will take appropriate actions.
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Home Chemistry Biochemistry. Credit: Nature Chemistry DOI: More information: Subhendu Bhowmik et al. This document is subject to copyright.
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View Wish List View Cart. Results for read theory Sort by: Relevance. You Selected: Keyword read theory. Grades PreK. Other Not Grade Specific. Higher Education. Adult Education. Digital Resources for Students Google Apps. Internet Activities. English Language Arts. Foreign Language. Social Studies - History. History World History. For All Subject Areas. See All Resource Types. Students will read about early theorists and complete comprehension and evidence based material. Each step is designed for scaffolding and targeting students learning styles.
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ReadingReading StrategiesClose Reading. Cooperative Learning. Read Theory Tracker Distance Learning. Read Theory tracker for students, parents and teachers to see what level students are completing passages on Read Theory. Once you set up an account, the program takes it over from there! It is adaptable, as in s. Not Grade Specific.The quest to create animals with human organs has a long history — and it is now becoming a reality.
Has science taken a step too far? They are naked apart from a few rags tied around their waist, with "fat, heavy, chinless faces, retreating foreheads, and a scant bristly hair upon their foreheads. As Pendrick approaches, they attempt to talk to him, but their speech is "thick and slopping" and their heads sway as they speak, "reciting some complicated gibberish".
Despite their clothes and their appearance, he perceives the "irresistible suggestion of a hog, a swinish taint" in their manner. They are, he concludes, "grotesque travesties of men". Wandering into Doctor Moreau's operating room one night, Pendrick eventually uncovers the truth: his host has been transforming beasts into humans, sculpting their bodies and their brains into his own image.
But despite his best efforts he can never eliminate their most basic instincts, and the fragile society soon regresses to dangerous anarchy, leading to Moreau's death.
It is years since Wells first published his novel, and to read some recent headlines you would think that we are veering dangerously close to his dystopic vision.
The hope is to implant human stem cells in an animal embryo so that it will grow specific human organs. The approach could, in theory, provide a ready-made replacement for a diseased heart or liver — eliminating the wait for a human donor and reducing the risk of organ rejection.
These bold and controversial plans are the culmination of more than three decades of research. These experiments have helped us understand some of the biggest mysteries of life, delineate the boundaries between species, and explore how a ragbag bunch of cells in the womb coalesce and grow into a living, breathing being. With new plans to fund the projects, we are now reaching a critical point in this research.
That is, provided we can resolve some knotty ethical issues first — questions that may permanently change our understanding of what it means to be human. For millennia, chimeras were literally the stuff of legend. The term comes from Greek mythology, with Homer describing a strange hybrid "of immortal make, not human, lion-fronted and snake behind, a goat in the middle". It was said to breathe fire as it roamed Lycia in Asia Minor.
In reality, chimeras in science are less impressive. The word describes any creature containing a fusion of genetically-distinct tissues.
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This can occur naturally, if twin embryos fuse soon after conception, with striking results. Consider the "bilateral gynandromorphs ", in which one side of the body is male, the other female. These animals are essentially two non-identical twins joined down the centre. If the two sexes have wildly different markings — as is the case for many birds and insects — this can lead to a bizarre appearance, such as a northern cardinal that had grown bright red plumage on half of its body, while the rest was grey.
Most often, however, the cells mix to form a subtler mosaic across the whole body, and chimeras look and act like other individuals within the species. There is even a chance that you are one yourself. The mixed bag of animals from Greek legends certainly cannot be found in nature. But this has not stopped scientists from trying to create their own hybrid chimeras in the lab. Janet Rossantthen at Brock University, Canada, was one of the first to succeed.
Inshe published a paper in the journal Science announcing a chimera that combined two mice species: an albino laboratory mouse Mus musculus and a Ryukyu mouse Mus carolia wild species from east Asia. View image of In the s mice chimeras were created from two species Credit: Naturepl.
Previous attempts to produce a hybrid "interspecific" chimera often ended in disappointment. The embryos simply failed to embed in the uterus, and those that did were deformed and stunted, and typically miscarried before they reached term. Rossant's technique involved a delicate operation at a critical point in pregnancy, around four days after mating.
At this point, the fertilised egg has divided into a small bundle of cells known as the blastocyst.If we can't tunnel through the Earth, how do we know what's at its center?Quiz - ReadTheory
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