The condition when an individual shows two or more genetically different cell lines that are derived from different zygotes, because of intermingling (see microchimerism). Chimerism on a micro scale is more common than generally appreciated, in the sense that most mothers who have had a child will, on careful investigation, be shown to have some white blood cells derived from their fetus or fetuses. See also mosaicism and mixoploidy, although most cases of chimerism do not cause an abnormality of the karyotype.

A state in an embryo, fetus, animal or person in which a small number of cells occur that have a different genome. Arises naturally because cells (rarely, stem cells) can cross between a mother and her fetus, or experimentally by introducing foreign stem cells into an embryo, usually at the stage of blastocyst, when the introduced cells become part of the inner cell mass.

An abnormal state of the chromosomes seen on a karyotype in which cells from an individual display two or more genetically different chromosome pattern. Can be the result of mosaicism or chimerism.