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Embryonic stem cells can differentiate into the three "germ layers": [[ectoderm]], [[endoderm]] and [[mesoderm]].  The 220 types of cells in humans are all based on these germ layers.  Some scientists have shown effectively that embryonic stem cells have greater differentiation potential, and divide into greater numbers, than [[adult stem cells]] can.
 
Embryonic stem cells can differentiate into the three "germ layers": [[ectoderm]], [[endoderm]] and [[mesoderm]].  The 220 types of cells in humans are all based on these germ layers.  Some scientists have shown effectively that embryonic stem cells have greater differentiation potential, and divide into greater numbers, than [[adult stem cells]] can.
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== Background ==
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Embryonic stem cells are pluripotent and thus can turn into any of the 3 germ layer types.<ref>http://learn.genetics.utah.edu/content/tech/stemcells/sctypes/</ref>
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Even though embryonic stem cells can differentiate into more cell types than can adult stem cells, like with in vitro fertilization, they require the destruction of the embryo, i.e. [[abortion]].  After harvesting embryonic stem cells, they can be cultured for an extended period of time and induced to proliferate without the need to destroy more embryos, though stem cell lines tend to drift genetically and become unusable after years of continuous culturing. New human embryonic stem cell lines are generated from the discarded embryos of in vitro fertilization clinics rather than the fertilization of human eggs for the express purpose of producing stem cell lines. There is some research that shows that embryonic stem cells might be obtainable without destruction of the embryo, though this research is not definite yet.<ref>http://www.cmda.org/AM/Template.cfm?Section=Stem_Cell_Research&TEMPLATE=/CM/ContentDisplay.cfm&CONTENTID=12577</ref>
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Largely driven by federal bans on using NIH funds to produce new human embryonic cell lines, much attention has been shifted away from embryonic stem cells to induced pluripotent stem cells (iPS cells). This type of cell is generated from adult (differentiated) cells though genetic manipulation and possess many of the properties of embryonic stem cells. iPS cells are a major leap forward in stem cell research and provide the distinct advantage of generating pluripotent stem cells from any adult individual. Thus, replacement cells and tissues generated from iPS cells can be immunologically compatible with the recipient if the iPS cells were initially germinated from cells donated by the recipient; this significantly reduces the risk of tissue rejection. This advancement in the stem cell field would not have likely come to pass this soon if not for the push to ban human embryonic stem cell research in the US.
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== History ==
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In 2001 President [[George W. Bush|Bush]] allowed [[federal funding]] for research performed only on the 60 human embryonic stem cell lines that were in existence at the time.<ref>https://www.whitehouse.gov/news/releases/2001/08/20010809-2.html</ref> Cell lines drift genetically and morphologically over time, and due largely to the ban on producing more embryonic stem cell lines with NIH funds, researchers focused on producing embryonic-like stem cells from adult (differentiated) cells; these cells are known and induced pluripotent stem cells (iPS cells). These cells have similar properties to embryonic stem cells but do no require the destruction of or any use of human embryos - humans donate their own cells (e.g. skin cells) and though slight genetic manipulation these cells, they can be reverted into essentially an undifferentiated state and gain the ability to become nearly any cell in the body (i.e. pluripotency). This major advance in the stem cell and medical fields came much sooner than most researchers expected; this can be credited largely to the Bush ban regarding human embryonic stem cells.  
 
In 2001 President [[George W. Bush|Bush]] allowed [[federal funding]] for research performed only on the 60 human embryonic stem cell lines that were in existence at the time.<ref>https://www.whitehouse.gov/news/releases/2001/08/20010809-2.html</ref> Cell lines drift genetically and morphologically over time, and due largely to the ban on producing more embryonic stem cell lines with NIH funds, researchers focused on producing embryonic-like stem cells from adult (differentiated) cells; these cells are known and induced pluripotent stem cells (iPS cells). These cells have similar properties to embryonic stem cells but do no require the destruction of or any use of human embryos - humans donate their own cells (e.g. skin cells) and though slight genetic manipulation these cells, they can be reverted into essentially an undifferentiated state and gain the ability to become nearly any cell in the body (i.e. pluripotency). This major advance in the stem cell and medical fields came much sooner than most researchers expected; this can be credited largely to the Bush ban regarding human embryonic stem cells.  
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