Mosaicism


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Related to Mosaicism: chimerism

Mosaicism

The coexistence of two or more genetically distinct cell populations derived originally from a single zygote. Mosaics may arise at any stage of development, from the two-cell stage onward, or in any tissue which actively proliferates thereafter. The phenomenon is commonly observed in many species of animals and plants and may be caused by somatic mutation or chromosomal nondisjunction. An individual animal or plant may exhibit mosaicism, or it may occur in a culture of a single cell- or tissue-type obtained from an individual.

Chromosome nondisjunction is probably the principal cause of chromosomal aberration, which in turn may lead to the development of mosaicism. During cell division, the two sister chromatids usually separate completely, each chromatid going to opposite poles of the cell guided by the spindle apparatus. In some cases, one chromatid will fail to completely separate, or it may lag behind. This nondisjunction will lead to the presence of both sister chromatids in the same daughter cell instead of one in each of the daughter cells (Fig. 1). Somatic crossing-over leads to the production of a recombinant mosaic where chromosome segments, with their corresponding blocks of genes, are exchanged between homologous chromosomes during mitosis. The occurrence of this process leads to mosaicism, mostly manifested as spots (clones of variant cells) on the cuticle of insects or on leaves, petals, or stamen hairs. See Chromosome

Mosaicism caused by chromosome nondisjunctionenlarge picture
Mosaicism caused by chromosome nondisjunction
Bilateral gynandromorphism in the moth Abraxas grossulariata enlarge picture
Bilateral gynandromorphism in the moth Abraxas grossulariata

Sex chromosome mosaicism, the presence of a mixture of cell populations with different X and Y chromosome constitutions, is not uncommon and is often seen in individuals with ovarian dysgenesis. The presence of a significant proportion of chromosomally abnormal cells in any such mosaic will tend to lead to a clinically expressed syndrome. The proportion of each constituent clone may vary from tissue to tissue, but is relatively stable in each individual site throughout adult life. Sex mosaics (gynandromorphs) are particularly striking where a difference in the secondary sexual characteristics exists between the normal sexes. For example, in a butterfly with bilateral gynandromorphism, the left side may show the characteristic wing color and pattern of the male, and the light wing, typical female patterning (Fig. 2). See Chimera, Genetics, Sex-linked inheritance

Mosaicism

 

the simultaneous presence in an organism of two or more varieties of homotypic cells differing in genetic structure, or genotype, and (or) in their manifestation of genes in the phenotype. Thus, in mosaicism, characters that are usually mutually exclusive (sex characters, color, biochemical features) appear simultaneously. Examples of mosaicism are bilateral or anterior-posterior mosaic insects or mosaic birds, mottled leaves in plants, red and white facets in the compound eyes of insects, the presence of XX and XY cells in the same individual and other anomalies of certain chromosomal diseases of humans.

Mosaicism results from the following conditions: (1) improper distribution of chromosomes in mitosis, (2) somatic mutations of gene and chromosome-type reconstructions, (3) somatic crossing-over, (4) redistribution of cytoplasmic genetic factors (for example, of plastids in plants) in such a way that they are lost in part of the cells, or (5) the functioning in different cells only of some one or other of the homologous chromosomes or of one of the allelic genes. One differentiates mosaicism based on changes in the genotype (conditions 1, 2, and 3) or plasmotype (condition 4). Phenotypic mosaicism is due to a change in the function of the gene or its dose (condition 5).

V. L. RYZHKOV

mosaicism

[mō′zā·ə‚siz·əm]
(genetics)
The coexistence in an individual of somatic cells of two or more genotypes or karyotypes; it is caused by gene or chromosome mutations, especially mitotic nondisjunction, after fertilization.
References in periodicals archive ?
This study presents the first evidence that fetal exposure of mice to a mutagenic chemical can directly result in an excess burden of mutations and increased mosaicism in both somatic tissues and germ cells of adult first filial generation (F1) mice.
ONeill, who works in the lab of Jeffrey Bush, PhD, captures these videos to help her decode the molecular steps that link Ephrin-B1 mosaicism to cell sorting.
Mosaicism in cell line samples with expansions such as those used here is very common, but is also observed in patient samples and can vary across tissues (16).
11) However, patients with mosaicism may survive beyond the first year of life.
In cases of mosaicism, 50–100 metaphases were scored.
As prenatal genetic diagnosis is possible and there is a risk that the syndrome will recur in subsequent pregnancies because of mosaicism, genetic counselling should be provided to the families of affected children.
Patients with 45,X/46,XY mosaicism can share clinical features with Turner syndrome, including short stature and cardiac anomalies.
It is believed that lines of Blaschko indicate somatic mosaicism reflecting the distribution of clones of abnormal keratinocytes during development.
Of the apparently de novo cases, some are due to germline mosaicism in the mother.
However, comparison with a suite of samples from elsewhere in the Scrag Lake pluton demonstrates that planar microstructures (some with possible decoration), kink banding, and grain mosaicism occur only in samples from the rim of the North structure and are similar to petrographic features observed in samples from the rim of the Bloody Creek structure.
In much the same way, Richardson argues that "cultural notions of females as complex, contradictory, and changeable" have influenced chromosomal studies of women, most notably in the case of X mosaicism theories of autoimmunity (p.