Definitions of some terms commonly used in the stem cell debate:
Adult stem cell -- A cell taken from mature tissue that can renew itself but has a limited ability to transform into specialized cell types.
Assisted reproductive technology -- Fertility treatments that involve a laboratory handling eggs or embryos, such as in vitro fertilization.
Blastocyst -- A preimplantation embryo of 30 to 150 cells.
Cloning -- The creation of an animal or person that derives its genes from a single other individual.
Differentiation -- The process by which early unspecified cells acquire the features of specific cells such as heart tissue, liver or muscle.
DNA -- The material that contains the instructions for making all the parts of the body.
Embryo -- The earliest stage of development from the single cell to implantation in the uterus.
Embryonic stem cell -- a cell from an embryo that has the potential to become a wide variety of specialized cell types.
Gene -- A unit of heredity that is a segment of DNA.
In vitro -- Done outside the body.
In vivo -- Done within the living body.
Nucleus -- The core of a cell that contains the chromosomes.
Stem cells -- Nonspecialized cells that have the capacity to self-renew and to differentiate into more mature cells.
Tissue or cell culture -- Growth of tissue in a laboratory dish for experimental research
Source: Department of Health and Human Services