Chimera

In medicine, a person composed of two genetically distinct types of cells. Human chimeras were first discovered with the advent of blood typing when it was found that some people had more than one blood type. Most of them proved to be "blood chimeras" — non-identical twins who shared a blood supply in the uterus. Those who were not twins are thought to have blood cells from a twin that died early in gestation. Twin embryos often share a blood supply in the placenta, allowing blood stem cells to pass from one and settle in the bone marrow of the other. About 8% of non-identical twin pairs are chimeras. Many more people are microchimeras and carry smaller numbers of foreign blood cells that may have passed from mother across the placenta, or persist from a blood transfusion. In vitro fertilization (IVF) is also contributing to the number of human chimeras. To improve success rates, two or more embryos are placed in the uterus so women who have IVF have more twin pregnancies than usual. More twins mean more chimeras. In Greek mythology, the Chimera was an awesome fire-breathing monster with the head of a lion, the body of a goat, and the tail of a serpent. The Chimera was killed by the hero Bellerophon mounted, in most versions of the tale, on Pegasus, the winged horse.

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1. In experimental embryology, the individual produced by grafting an embryonic part of one animal on to the embryo of another, either of the same or of another species. 2. An organism that has received a transplant of genetically and immunologically different tissue, such as bone marrow. 3. Dizygotic twins that retain each other as immunologically distinct types of erythrocytes. 4. A protein fusion in which two different proteins are linked via peptide bonds; usually genetically engineered. Chimeric antibodies may have the Fab fragment from one species fused with the Fc fragment from another. 5. Any macromolecule fusion formed by two or more macromolecules from different species or from different genes. [L. Chimaera, G. Chimaira, mythic monster (lit. a she-goat)]

- radiation c. an individual that has been subjected to whole body irradiation in order to lower immune response to foreign donor cells and therefore has the immunologic characteristics of both host and donor after a bone marrow graft from the antigenically different donor.

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chi·me·ra or chi·mae·ra kī-'mir-ə, kə- n an individual, organ, or part consisting of tissues of diverse genetic constitution Chimera Greek mythological character. The Chimera was a fire-breathing she-monster made up of the front parts of a lion, the middle parts of a goat, and the tail of a snake.

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chi·me·ra (ki-mērґə) [Gr. chimaira a mythological fire-spouting monster with a lion's head, goat's body, and serpent's tail] 1. an individual organism whose body contains cell populations derived from different zygotes, of the same or of different species; it may occur spontaneously, as in twins (blood group chimeras), or be produced artificially, as an organism that develops from combined portions of different embryos, or one in which tissues or cells of another organism have been introduced. Cf. mosaic. 2. a substance created from proteins or genes of two species, as by genetic engineering. chimeric adj