Glossary main content.


adult stem cell

An undifferentiated cell found in people of any age that is preprogrammed to develop into other cell types. Adult stem cells can only develop into the types of cells present in the tissue in which they reside.


A building block of a DNA molecule. There are four types of bases: adenine (A), thymine (T), cytosine (C), and guanine (G).

base pair

A pair of bases weakly bound together to make a unit in double-stranded DNA.

beta cell

An insulin-producing cell in the pancreas.


An embryo four or five days after fertilization. At this stage, the embryo’s cells are undifferentiated.


The fundamental microscopic unit that is the building block of all living things except viruses.


The structure in a cell's nucleus that contains DNA. Human cells have 46 chromosomes—23 from each parent.


The part of the cell that contains all cellular components except the nucleus.

development (biological)

The process by which organisms and their biological components change over time, especially in the earliest stages.


A disease which leaves the body unable to make or use sufficient amounts of the hormone insulin. This disrupts the person’s ability to convert carbohydrates in the diet to glucose, the body’s fuel. There are two kinds of diabetes: Type 1, or “early-onset,” and Type 2, or “adult-onset.”


When cells become specialized in form and function.

DNA (deoxyribonucleic acid)

A molecule found in almost every cell that contains an organism's genetic code. DNA is made of two strings of bases wound in a helix, or spiral, shape.


A female reproductive cell.


An unborn offspring undergoing development. In humans, an embryo is considered a fetus after the eighth week of gestation.

embryonic stem cell

A stem cell derived from the inner cell mass of a blastocyst or from a reproductive cell (egg or sperm). Embryonic stem cells can develop into any kind of cell in the body.


A specific sequence of DNA bases which codes for the expression of one or more traits.


The scientific study of heredity. Also, the genetic constitution of an individual, group, or class.


A chemical or protein that acts as a messenger or signal to stimulate activity in the body.

immune system

The components of the body that prevent and fight disease.


A hormone produced by the pancreas that regulates the amount of glucose in blood.


The structure of a cell that contains DNA in the form of chromosomes.


Having the capacity to become any kind of cell or tissue in the body.

reproductive cloning

Using the technique of somatic cell nuclear transfer to create an embryo that will develop to term. The offspring would be a clone of the organism whose nuclear DNA was inserted into the donor egg cell.

somatic cell nuclear transfer

The technique of transferring a nucleus from one cell into an egg that has had its nucleus removed.

stem cell

A cell that has the ability to develop into different kinds of cells or tissues.

stem cell line

A group of stem cells originating from a single individual that are continually replicating in culture.

therapeutic cloning

Using the technique of somatic cell nuclear transfer to create an embryo from which stem cells are derived for the purpose of studying development and disease.


A group of cells in the body specialized for a certain function.


Any characteristic that is observable and measurable. Traits can be determined genetically, environmentally, or from a combination of the two.