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 ?
Distribution of 3PN embryo Chromosomal status n % Normal (euploid/diploid) 10 33.3 Abnormal 20 66.7 Aneuploidy 3 10.0 Triploidy 13 43.3 Mosaicism 4 13.3 Total 30 100
On a molecular scale, a selection of the observed long-lived cells contained protein complexes displaying age mosaicism. For example, the primary cilia (hair-like appendages on the outside of cells) of beta cells in the pancreas and neurons contained protein regions of vastly different lifespans.
This was quite surprising since mosaicism in PKS is rarely diagnosed in peripheral lymphocytes.
The predominant underlying cause of intraorganismal genetic variation was attributed to somatic mutations, and our results highlight potential mechanisms contributing to this genetic mosaicism. Mutation frequency increased in corals of greater size and in those occupying shallower depths.
Mosaicism for a small supernumerary ring X chromosome in a dysmorphic, growth-retarded male: mos47,XXY/48,XXY, +r(X).
Linear and whorled naevoid hypermelanosis in a patient with trisomy 4 mosaicism. Clin Exp Dermatol 2015;40(1):45-7.
According to the company, Dr Chun has identified the first lysophospholipid receptor (1996), first to demonstrate genomic mosaicism in the brain (2001) and its alteration in Alzheimer's disease (2015).
In this situation, the detection of mosaicism is essential.
Although IP is mostly a male lethal syndrome, it rarely occurs in males with Klinefelter syndrome or a genomic mosaicism. Gupta et al.
The very low-level mosaicism for monosomy 13 (3/117) in this case supports this perspective.
With controlled timing, gene editing was restricted to only the paternal pathogenic mutation, resulting in 72% of all injected embryos having two normal copies of the gene in all cells without any mosaicism. Whole-genome sequencing revealed no additional mutations above the detection limit of the assay.