Stem cells are a class of undifferentiated cells that are able to differentiate into specialized cell types. Commonly, stem cells come from two main sources:
-Embryos formed during the blastocyst phase of embryological development (embryonic stem cells)
-Adult tissue (adult stem cells)
Both types are generally characterized by their potency, or potential to differentiate into different cell types (such as skin, muscle, bone, etc.).
Stem cells are either extracted from adult tissue or from a dividing zygote in a culture dish. Once extracted, scientists place the cells in a controlled culture that prohibits them from further specializing or differentiating but usually allows them to divide and replicate. The process of growing large numbers of embryonic stem cells has been easier than growing large numbers of adult stem cells, but progress is being made for both cell types.
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