Mosaic

An individual or tissue containing two or more types of genetically different cells. All females are mosaics because of X-chromosome inactivation (lyonization). Mosaic patterns can affect how genetic disorders are expressed. For example, about 5 percent of people with Down's syndrome have a mosaic variant, where only some cells have an extra chromosome 21. These individuals have fewer clinical symptoms, are more likely to have a normal IQ, and are less likely to have heart and other problems that can be associated with Down syndrome.

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1. Inlaid; resembling inlaid work. 2. The juxtaposition in an organism of genetically different tissues; it may occur normally (as in lyonization, q.v.), or pathologically, as an occasional phenomenon. From somatic mutation (gene mosaicism), an anomaly of chromosome division resulting in two or more types of cells containing different numbers of chromosomes (chromosome mosaicism), or chimerism (cellular mosaicism). [Mod. L. mosaicus, musaicus, pertaining to the Muses, artistic]

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mo·sa·ic mō-'zā-ik n an organism or one of its parts composed of cells of more than one genotype: CHIMERA

mosaic adj

1) exhibiting mosaicism

2) DETERMINATE

mo·sa·i·cal·ly -'zā-ə-k(ə-)lē adv

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mo·sa·ic (mo-zaґik) [Gr. mouseion, from mousa, Muse] 1. a pattern made of numerous small pieces fitted together. 2. in genetics, an individual composed of two or more cell lines that are karyotypically or genotypically distinct but are derived from a single zygote. Cf. chimera. 3. in embryology, the condition in the fertilized eggs of some species, such as the sea urchin, whereby the cells of early stages have developed cytoplasm which determines the parts that are to develop. 4. in plant pathology, a viral disease characterized by mottling of the foliage.