Review paper revised final


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Review paper revised final

  1. 1. Universidad de Puerto Rico, Recinto de Cayey,<br />Colegio de Ciencias,<br />Cayey, Puerto Rico<br />Ivan J. Garcia, RISE Program<br />December 2010<br />Animal hybridization and Chimeras: Effects and Consequences of an Alternating Generation<br />___________________________________________________________________<br /><ul><li>Abstract
  2. 2. Animal Hybridization has always been controversial and dangerous for nature. A hybrid in theory is a cross-bread organism of two different subspecies of the same Superclass or Phylum. Chimeras cannot be mistaken with hybrids, and their composition goes beyond that of a cross-breed between subspecies. A Chimera is an organism cross-breed with parts of two completely different organisms, from two distinct Phylum or Superclass’s, for example a pig which circulates human blood. Hybrids and Chimeras go against natural selection and disrupt the flow of nature itself. Hybrids where, until recently, only existing in captivity, but recent events and discoveries have led scientist to believe that animals are cross-breeding in nature without any outside stimulation; thus starting to alter some ecosystems, while scientist in laboratories are creating experimental chimeras that could present severe dangers to ecosystems and organisms alike. </li></ul>_____________________________________________________________________________________<br /><ul><li>Hybrid salvation
  3. 3. Hybridization may be the key for species facing extinction. Because of the continuing effects of global warming, there is a concurring hypothesis in the scientific community, in which most of the arctic ice will melt in the next 20 years. Species may hybridize in order to survive on warmer temperatures and even on land. A good example of this hybridization is the offspring from a polar bear and a grizzly bear; this species can survive on the same conditions as a grizzly bear, while retaining most of the polar bear traits. Whales are slowly hybridizing, by naturally mating with different species in the wild. Unlike hybrids breed in captivity, natural hybrids have a higher (and they already do, and it happens uncommonly) can reproduce; meaning there are born fertile hybrids. Although species might change completely, it can be a vital way for them to keep living and not get extinct. The only way a hybrid species can survive, is if they can find a way around their infertility.
  4. 4. Fig. 1 shows a liger (a lion and tiger hybrid), and its unusual big size.
  5. 5. 5213355651500
  6. 6. Reproductive Isolation
  7. 7. Male hybrids created through speciation and hybridization are usually infertile. Research says it is a reproductive isolation which occurs in different stages of cell development in a process called spermatogenesis (Oka, 2010). The animals showed this spermatogenesis in a pre-meiotic stage, metaphase I and prophase I. In the past it was thought that the allele (gene) that affected this sterilization was responsible only in one stage, now it is known it acts on these three stages. They constructed a strain called B6-ChrXMSM (Oka et al. 2004), which contained the X chromosome of one of the mice. Results show that this spermatogenesis reduces sperm quantity and quality, smaller testis, and in rare occasions incompatible gametes; some also failed to even complete the meiotic process. In all the tests sterile hybrids where made, even in the ones with compatible gametes. With the knowledge gained in this research, scientist can now make up a technique or strain to help these hybrids complete their meiosis healthy and completely in order to create fertile hybrids (or at least in a F2 generation).
  8. 8. Incompatible Genes
  9. 9. For years reasonable answers have been sought after the intriguing question of, why diverged animals produce weak hybrids. It has been known for some time now why hybrids are born infertile, but the reason for their weakness and slower development (anonymous, 2008) was still in the shadows of scientific investigations. Researches placed copepod hybrids in a controlled environment replicating real life situations. The results showed that the hybrid copepods where not able to adapt to the climatic changes in time for them to survive. They compared the genetic codes for the normal copepod and the hybrid, resulting in a shocking conclusion. Their RNA polymerase failed to trigger the changes needed to survive (anonymous, 2008). This also concludes that when hybrids are made, genes can be incompatible with each other due to speciation.
  10. 10. Human/Animal Chimeras
  11. 11. In ancient Greek mythology a Chimera is a combination of three animals in one body; in the modern age it’s the combination of human parts (DNA, cells, tissues, etc.) and animal parts in one body. Although considered unethical, inhumane and even dangerous by many (it has been banned in Canada); it is a practice that according to other scientist might hold the key for future medicines and treatments. Examples of modern chimeras include rats with 1% human brain (future experiments will try to increase that percent to 100), the fusion of human cells in rabbit eggs, pigs with circulating human blood, and human tissues inside animal bodies for surgical uses. Scientists are also using these chimeras to test drugs and medicinal procedures and treatments, so they can be later performed, if successful, in real humans. They believe that if animals have more human aspects and physiological traits they can better understand drugs and see more real-life reactions. Although it may seem perfect for medicinal uses, there are many concerns with this; starting with the simple fact that, how can that animal/chimera be classified, human or an animal? What kind of laws could help protect these chimeras? Many disasters can happen from this, starting with the fact that this is altering the course of natural selection, natural habitats, and animals and humans themselves.
  12. 12. Legal human-animal hybrids
  13. 13. Whether it’s considered ethical or unethical, scientist could be licensed to work with animal-human hybrid embryos. But there are certain limitations to this licensing; for example these embryos could be used for stem cell research, but no true hybrids could be created (half human, half animal), basically a chimera can’t be made. These so called legal hybrids where given the name of cytoplasmic hybrids. These are strictly research intended and although are legal, it is illegal to manipulate them to alter their genetic sequence after such stages of hybridization.
  14. 14. Conclusion
  15. 15. Hybrids and Chimeras should not exist in the natural world, as it will disrupt the course of nature. It may sound contradicting, but hybrids, although just bound to disrupt the course of nature, could be the only salvation for several species of animals. Overcoming the infertility in mitosis might prove to create a new species from several hybrids. Future studies should further discovery why hybrids are weaker than their fellow originals. Chimeras on the other hand are said to be used for medical studies and development, but it is anti-ethical and contrary to hybrids can permanently change and destroy ecosystems. Chimeras are on the brink of being eradicated and banned from many countries. Illegal in most countries, specializations of hybridizations have been made strictly for cytoplasmic hybridization.
  16. 16. Bibliography
  17. 17. 1). George, Jane. "Warming Arctic Will Give Rise to Mammal Hybrids: Biologist." Vancouver Sun | Latest Canada Daily News. 28 Apr. 2010. Web. 06 Oct. 2010. <>.
  18. 18. 2). Mott, Maryann. "Animal-Human Hybrids Spark Controversy." Daily Nature and Science News and Headlines | National Geographic News. 25 Jan. 2005. Web. 15 Oct. 2010.
  19. 19. 3). Oka, Ayako, and Akihiko Mita, et. Al., "Reproductive Isolation in Hybrid Mice Due to Spermatogenesis Defects at Three Meiotic Stages." ProQuest Biology Journals. ProQuest, Sept. 2010. Web. 23 Oct. 2010. <http://>.
  20. 20. 4). Anonymous. "Cause of Weakness in Marine Animal Hybrids Discovered." ProQuest, Nov. . Web. 7 Nov. 2010. http://
  21. 21. 5). The Lancet. "Animal-human Hybrid-embryo Research." ScienceDirect, 13 Sept. 2007. Web. 10 Dec. 2010. <http://>.