Adult stem cells

Stem cells which are already committed to becoming a certain cell type, but have not yet done so. Ie, blood stem cells will be in your blood stream, ready to turn into blood cells when needed, but as yet have not done so. As with all stem cells, not only can Adult stem cells turn into the cell type they are predestined to, but they can also replicate themselves so that the body has a constant supply. Scientists are unclear as to whether or not these cells can give rise to cell types other cell types in the body.

Blastocyst

One stage before an embryo – this is preimplantation and is a cluster of cells, around 30-150 in number. The blastocyst consists of a sphere made up of an outer layer of cells (the trophectoderm), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass).

Cell division

Method by which a single cell divides to create two cells (an exact copy).

Cell line

Cells that can be grown and maintained in a medium culture (nutrient solution) which appear to regenerate and have an indefinite life span.

Chimera

An organism composed of cells derived from at least two genetically different zygotes, from the same or different species. Chimerism can be produced experimentally at different stages of development, from embryo through to adult.

Chromosomes

The structures within the nucleus that consist mostly of DNA and determine the genetic makeup of the organisms. Chromosomes contain genes, working subunits of DNA that carry the genetic code for specific proteins, interspersed with large amounts of DNA of unknown function. A normal human body cell contains 46 chromosomes, half of which are contributed by the father and half by the mother.

Clone

Generation of a cell which is genetically identical to the original cell.

Cloning

Generation of an embryo by somatic cell nuclear transfer.

Differentiation

The process by which stem cells acquire characteristics and form more specialized cell types (ie blood, bone, muscle).

Directed differentiation

Coaxing stem cells to differentiate into different cell types.

DNA

Deoxyribose nucleic acid; the genetic material of the chromosomes.

Embryo

An organism in the early stages of development; in humans, up to about 6 weeks of development.

Embryonic stem (ES) cells

Pluripotent stem cells derived from the inner cell mass of a blastocyst stage embryo.

Fetus

An organism from the end of the embryonic period ( 6 weeks of development in the human), up to birth.

Gamete

The sex cell (sperm or egg). The functional, mature, male gamete is called a sperm while the female gamete is called the ovum, or egg.

Gamete provider

A person who is a biological parent of the embryo, but does not necessarily have custody of the embryo or any authority to make decisions regarding its disposition.

Gonad

An organ that produces sex cells (a testis or an ovary).

Hematopoietic

Related to the formation of blood cells, a process that occurs mainly in the bone marrow.

Hematopoietic stem cell

Precursors of mature blood cells that give rise to all red and white blood cells and platelets.

Human embryonic stem cell (hESC)

A type of pluripotent, self-renewing stem cell which is derived from the inner cell mass of a developing blastocyst.

In vitro fertilization (IVF)

Fertilization of an egg by a sperm outside a woman's body.

Inner cell mass

A small cluster of cells within the blastocyst.

Mitosis

Cell division.

Multipotent

The ability of a cell type to change into more than one type of cell within the body but not fully pluripotent.

Neural

Related to the cells of the nervous system.

Nucleus

The portion of the cell enclosing the genetic material of the chromosomes.

Oocyte

An immature ovum (egg).

Ovum

See "gamete".

Plasticity

The ability of one cell type from one tissue type to generate another cell type of another tissue.

Pluripotent stem cell

A stem cell with the capacity to differentiate into cells of all germ layers (endoderm, ectoderm, and mesoderm). These are usually derived from early embryos or embryonic germ cells.

Progenitor cell

A cell type that can differentiate, but not regenerate, and cannot renew itself.

Regenerative medicine

Using stem cells to replace damaged cells and tissue.

Reproductive cloning

Creating a fetus through somatic cell nuclear transfer from a cell which is genetically identical to the cell donor.

Somatic cell nuclear transfer

Nuclear transfer, nuclear replacement: see 'cloning'; The transfer of a nucleus from a somatic cell into an unfertilized egg (oocyte) which has had its nucleus removed (i.e. has been 'enucleated').

Somatic cells

The cells of an organism, other than those cells whose descendants may include gametes.

Sperm

See "gamete".

Stem cell

A cell that has the ability to divide for indefinite periods in culture and to give rise to specialized cells.

Stromal cell

A cell from the body other than gamets.

Therapeutic cloning

Somatic cell nuclear transfer in order to produce embryonic stem cells which are an exact match to the donor. The donor's somatic cells are implanted into an enucleated egg. The embryonic stem cells are then harvested, and may be used to coaxed to differentiate into a particular cell type, and used to repair damaged tissue.

Totipotent cells

Transdifferentiation

The process by which a cell from one tissue may differentiate into a cell type of another tissue.

Umbilical cord blood stem cells

Small amounts of hematopoietic stem cells which may be harvested from the umbilical cord at birth. These cells are similar to those residing within the bone marrow, and may be used for the treatment of leukemia, and other diseases of the blood.

Zygote

A fertilized egg formed as a result of the union of the male (sperm) and female (egg) sex cells.