1. The type of stem cell which the article mainly discusses is the embryonic stem cell. Sperm and egg undergo fertilization form a zygote. A zygote then divides into many cells through cell division, and these cells form what's called embryos after division and differentiation. It is after differentiation that each embryo acquires a specific function, only able to form certain cell types such as muscle or bone. The scientific principle behind stem cells is that this embryo, once not having underwent differentiation, is capable of becoming any of the 220 cell types in the human body. By extracting those 'pluripotent' embryos and growing them seperately, we are able to obtain the embryonic stem cells which can be used to regenerate damaged tissues and organisms.
Another type of stem cell, perhaps the more orthodox and uncontroversial among the two, is the adult stem cell. Adult stem cells are yet undifferentiated cells that are capable of differentiating into specific organisms if necessary. Unlike embryonic stem cells, adult stem cells inherently exist in the human body (usually in the marrows) in extremely small amounts, and are incapable of forming all cell types with no limitations. One renowned example of an adult stem cell existing in our bodies is the Hematopoietic Stem Cell, widely used in bone-marrow transplantation among leukemia patients.
The newly developed iPCS perhaps epitomizes the cutting edge stem cell technology of the era--iPCS, first found by Prof. Yamanaka of Kyoto University, refers to the specially manipulated somatic cells that are literally 'reprogrammed' to function as differentiable embryonic cells. Enabling such is the transplantation of embryonic genes into the somatic cells through the use of retroviruses, the 'carriers' of the genes. The efficiency of iPCS method is an absolutely unparalleled one, for conventional methods of reprogramming involed an extremely elaborate process by which the genetic material from an adult cell is injected into an egg cell whose DNA has been removed.
2. Though it requires great precision, cloning, in its essence, is an extremely straightforward process. First you remove the nucleus from the fertilized egg, and replace the removed nucleus with a nucleus obtained from a cell of another living organism. Since the DNA information of the egg would then also be replaced with that of the nucleus donor, the offspring generated afterwards would be the exactly identical 'clone' of the donor.
3. The ethical question regarding stem cells is whether we should view the embryo as a seperate, independent living organism. The embryo itself is often destroyed when its pluripotent portion is extracted and seperated. Many Christians (mainly the Catholics) have spearheaded the anti-embryonic stem cell movement for they view an embryo as a basic form of life with spirit, and therefore believe that the destruction of such embryo is equivalent to murder. However, as the innovate iPCS method has rised, many of the ethical controversies about stem cells have generally diminished.
+Egg donor problem; black market? --also solved thanks to iPCS
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