Are
derived from embryos.
Specifically, embryonic stem cells are derived from embryos that develop from
eggs that have been fertilized in vitro, in an in vitro
fertilization clinic, and then donated for research purposes with informed
consent of the donors. They are not derived from eggs fertilized in a
woman's body. The embryos from which human embryonic stem cells are derived are
typically four or five days old and are a hollow microscopic ball of cells
called the blastocyst. stem
cell is an undifferentiated cell found among differentiated cells in a tissue
or organ, can renew itself, and can differentiate to yield the major
specialized cell types of the tissue or organ. The primary roles of adult stem
cells in a living organism are to maintain and repair the tissue in which they
are found. Some scientists now use the term somatic stem cell instead of adult
stem cell. The origin of adult stem cells in mature tissues is unknown
