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Stem-Cells

Almost everyday there are news stories about the latest developments in cloning and stem-cell science. Encouraged by the excitement, some companies have formed which offer the storage of DNA samples or umbilical cords. Reputable scientists have released promising results on stem-cell research and contemporaneously, religious cults or "rogue" scientists have made unverified claims regarding their cloning successes. As a result, the lay-person is faced with an increasingly complicated picture of stem-cell research and cloning, meaning that because the basic science is not understood, ethical assessments can easily be distorted. It is necessary for a solid ethics of ontogeny that this basic science is clear to the majority of people.

Stem-cells can differentiate into many different kinds of cells. There are three different types of stem-cell: totipotent, pluripotent, and multipotent. Totipotent stem-cells are the first kind of cell created by conception and constitute the zygote (a hollow cellular structure of around 100 stem-cells that develops after conception). They contain complete genetic information and consequently can turn into any cell, including other kinds of stem-cell. In the following few days after conception, totipotent stem-cells transform into pluripotent stem-cells and trophoblast cells. Pluripotent cells constitute the blastocyst (inner layer) of the growing zygote, and when harvested can transform into any cell of the human embryo. The trophoblast (outer-layer) cells transform into the placenta, umbilical cord, and amniotic sac. The inner, pluripotent cells then become increasingly specialized and transform into the multipotent stem-cells that constitute the embryo. Multipotent stem-cells have a more limited range of what types of cells they can turn into as they arise in embryonic development, defining different organs and tissues. The totipotent and pluripotent types of stem-cell are more efficient and utilizable in medical research whereas multipotent stem-cells are more difficult to employ because of their limitations.

These three types of stem-cell are derived from five sources: cryopreserved embryos, therapeutic cloning, fetal germ cells, umbilical cords, and people. Totipotent stem-cells can be harvested from zygotes, though the harvesting destroys the zygote. These zygotes can be thawed from cryopreservation, having been left-over from invitro-fertilization (IVF) treatments, or they can be created by therapeutic cloning. Therapeutic cloning involves implanting a patient's DNA into a donated human ova, emptied of its original DNA (a process called "somatic cell nuclear transfer"). The ova is made to divide with the DNA replacement inside, creating a zygote and making totipotent stem-cells available for harvesting. Unlike stem-cells from cryopreserved embryos, these stem-cells match the patient's DNA, making the rejection of cells transplanted to the patient unlikely. In contrast, only the pluripotent type of stem-cells can be harvested from fetal germ cells, which are usually taken from aborted feti that have been donated to medicine. Multipotent stem-cells are harvested from umbilical cords and people, and though they are more limited in their uses, they will match the patient's DNA if the source is the patient or the patient's umbilical cord.

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