Human Cloning and Human Dignity:
An Ethical Inquiry
The President's Council on Bioethics
Washington, D.C.
July 2002
www.bioethics.gov
Glossary of Terms
Asexual reproduction
Reproduction not initiated by the union of oocyte and sperm. Reproduction in which all (or virtually all) the genetic material of an offspring comes from a single progenitor.
Blastocyst
Name used for an organism at the blastocyst stage of development.
Blastocyst stage
An early stage in the development of embryos, when (in mammals) the embryo is a spherical body comprising an inner cell mass that will become the fetus surrounded by an outer ring of cells that will become part of the placenta.
Cloned embryo
An embryo arising from the somatic cell nuclear transfer process as contrasted with an embryo arising from the union of an egg and sperm.
Cloning
- Cloning-to-produce-children-Production of a cloned human embryo, formed for the (proximate) purpose of initiating a pregnancy, with the (ultimate) goal of producing a child who will be genetically virtually identical to a currently existing or previously existing individual.
- Cloning-for-biomedical-research-Production of a cloned human embryo, formed for the (proximate) purpose of using it in research or for extracting its stem cells, with the (ultimate) goals of gaining scientific knowledge of normal and abnormal development and of developing cures for human diseases.
- Gene (molecular) cloning-Isolation and characterization of DNA segments coding for proteins (genes) using carrier pieces of DNA called vectors.
- Human cloning-The asexual reproduction of a new human organism that is, at all stages of development, genetically virtually identical to a currently existing, or previously existing, human being.
Chromosomes
Structures inside the nucleus of a cell, made up of long pieces of DNA coated with specialized cell proteins, that are duplicated at each cell division. Chromosomes thus transmit the genes of the organism from one generation to the next.
Cytoplasmic
Located inside the cell but not in the nucleus.
Diploid
Refers to the chromosome number in a cell, distinct for each species (forty-six in human beings).
Diploid human cell
A cell having forty-six chromosomes.
Embryo
- The developing organism from the time of fertilization until significant differentiation has occurred, when the organism becomes known as a fetus.
- An organism in the early stages of development.
Enucleated egg
An egg cell whose nucleus has been removed or destroyed.
Epigenetic modification
The process of turning genes on and off during cell differentiation. It may be accomplished by changes in (a) DNA methylation, (b) the assembly of histone proteins into nucleosomes, and (c) remodeling of chromosome-associated proteins such as linker histones.
Epigenetic reprogramming
The process of removing epigenetic modifications of chromosomal DNA, so that genes whose expression was turned off during embryonic development and cell differentiation become active again. In cloning, epigenetic reprogramming of the donor cell chromosomal DNA is used to reactivate the complex program of gene expression and repression required for embryonic development.
Eugenics
An attempt to alter (with the aim of improving) the genetic constitution of future generations.
Gamete
A reproductive cell (egg or sperm).
Haploid human cell
A cell such as an egg or sperm that contains only twenty-three chromosomes.
Infertility
The inability to conceive a child through sexual intercourse.
In vitro fertilization (IVF)
The union of an egg and sperm, where the event takes place outside the body and in an artificial environment (the literal meaning of "in vitro" is "in glass"; for example, in a test tube).
Mitochondria
Small energy-producing organelles inside of cells. Mitochondria give rise to other mitochondria by copying their small piece of mitochondrial DNA and passing one copy of the DNA along to each of the two resulting mitochondria.
Moral status
The standing of a being or entity in relation to other moral agents or individuals. To have moral status is to be an entity toward which human beings, as moral agents, have or can have moral obligations.
Multipotent cell
A cell that can produce several different types of differentiated cells.
Nucleus
An organelle, present in almost all types of cells, which contains the chromosomes.
Nuclear transfer
Transferring the nucleus with its chromosomal DNA from one (donor) cell to another (recipient) cell. In cloning, the recipient is a human egg cell and the donor cell can be any one of a number of different adult tissue cells.
Oocyte
Egg.
Organism
Any living individual animal considered as a whole.
Parthenogenesis
A form of nonsexual reproduction in which eggs are subjected to electrical shock or chemical treatment in order to initiate cell division and embryonic development.
Pluripotent
A cell that can give rise to many different types of differentiated cells.
Somatic cell (human)
A diploid cell containing forty-six chromosomes obtained or derived from a living or deceased human body at any stage of development.
Somatic cell nuclear transfer (SCNT)
Transfer of the nucleus from a donor somatic cell into an enucleated egg to produce a cloned embryo.
Stem cells
Stem cells are undifferentiated multipotent precursor cells that are capable both of perpetuating themselves as stem cells and of undergoing differentiation into one or more specialized types of cells.
Totipotent
A cell with an unlimited developmental potential, such as the zygote and the cells of the very early embryo, each of which is capable of giving rise to (1) a complete adult organism and all of its tissues and organs, as well as (2) the fetal portion of the placenta.
Zygote
The diploid cell that results from the fertilization of an egg cell by a sperm cell.
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