allows the cells to continue dividing (replicating) in culture indefinitely.


– See Comparative genomic hybridization


– An organism composed of cells derived from at least two genetically different individuals.


– The outermost of the two membranes surrounding the embryo/fetus, part of which forms the fetal portion of the placenta.

Chorionic villus sampling (CVS)

– A prenatal test performed by removing a small sample of the placenta from the uterus with either a catheter (a thin flexible tube) or a needle. The sample can be tested for genetic abnormalities. Chorionic villus sampling is usually done between the 10th and 12th weeks of pregnancy.


– Structures composed of very long DNA molecules (and associated proteins) that carry most of the hereditary information of an organism. Chromosomes are divided into functional units called genes, each of which contains the genetic code (instructions) for making a specific protein. A normal human body cell (somatic cell) contains 46 chromosomes; a normal human reproductive cell (gamete) contains 23 chromosomes.


– The process of cell division in the very early embryo before it becomes a blastocyst.

Cleavage pattern

– The pattern in which cells in a very early embryo divide; each species of organism displays a characteristic cleavage pattern that can be observed under a microscope. Departure from the characteristic pattern usually indicates that an embryo is abnormal, so cleavage pattern is used as a criterion for preimplantation screening of embryos.


– 1) An exact genetic replica of a DNA molecule, cell, tissue, organ, or entire plant or animal. 2) An organism that has the same nuclear genome as another organism.


– The production of a clone. (For the purpose of this report, generating an individual animal or person that derives its nuclear genes from a diploid cell taken from an embryo, fetus, or born individual of the same species.)

Comparative genomic hybridization (CGH)

– A chromosomal screening technique that permits the detection of quantitative changes in chromosomal copy number without the need for cell culturing. It provides a global overview of chromosomal gains and losses

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement