In medicine (genetics), a mosaic or mosaicism denotes the presence of two populations of cells with different genotypes in one patient, where usually one of the two is affected by a genetic disorder. Mosaicism may result from a mutation during development which is propagated to only a subset of the adult cells. Mammalian females are usually mosaic because one of their X chromosomes is randomly inactivated during development.
Although the two can have some common symptoms, mosaicism is distinctly different from chimerism; in the latter, two or more cell lines of different origin are present in an organism and are not simply the result of mutation within a single cell line.
Although most forms of trisomy are due to problems in meiosis and affect all cells of the organism, there are cases where the trisomy only occurs in a selection of the cells. This is usually due to a nondisjunction event in an early mitosis. Generally this leads to a milder phenotype than in non-mosaic patients with the same disorder.
Sometimes intersex conditions can be caused by mosaicism - where some cells in the body have XX and others XY chromosomes.
Another example of a mosaic genotype is one of the milder forms of Klinefelter syndrome, called 46/47 XY/XXY mosaic wherein some of the patient's cells contain XY chromosomes, and some contain XXY chromosomes. The 46/47 annotation indicates that the XY cells have the normal number of 46 total chromosomes, and the XXY cells have 47 total chromosomes.
A special type of mosaicism is gonadal mosaicism. This is when a part of the gonadal cells of an organism have different genotype than the rest of the cells, usually because of a mutation that occurred in an early stem cell that gave rise to a part or all of the gonadal tissue. If these cells have sustained a new mutation that causes a dominant heritable disease, then it is possible for two healthy parents to have an offspring suffering from the disease. Usually when this happens it is because of a new mutation in the zygote, but if the parents have two or more offspring with the same disorder, then it is an indication of gonadal mosaicsm.
- Readers may use this email link to report errors and/or omissions they have discovered, or to add additional material or comments regarding this article "Mosaicism"
- Wiki Staff should discuss this article in the Wiki Staff Forum
- Susan's Place Transgender Resources Forums
- Susan's Place Transgender Chat
Browse: Gender | Cross-dressing | Intersexuality | Transgender topics | Transsexualism | Hormone Therapy | Surgery | Standards of Care | Legal Information | Psychology | Transitioning | Family & Friends | People | Books | Abbreviations | Browse All TopicsRead the FAQ | Return to the Main Page
Want to help us? Write New Articles and/or Expand Current Articles
*Some information provided in whole or in part by http://en.wikipedia.org/