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Encyclopedia > Mosaic (genetics)

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. This article is about the field and science of medical practice and health care. ... Genetics (from the Greek genno γεννώ= give birth) is the science of genes, heredity, and the variation of organisms. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hook from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ... The genotype is the specific genetic makeup (the specific genome) of an individual, in the form of DNA. Together with the environmental variation that influences the individual, it codes for the phenotype of that individual. ... A genetic disorder, or genetic disease, is a disease caused by abnormal expression of one or more genes in a person causing a clinical phenotype. ... In biology, mutations are changes to the genetic material (either DNA or RNA). ... Morphogenesis is also the name of a band. ...


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. In zoology, chimera is an animal which has two or more different populations of genetically distinct cells that originated in different zygotes; if the different cells emerged from the same zygote, it is called a mosaicism. ...


Although most forms of trisomy are due to problems in meiosis and affect all cells of the organism, there are cases where la, la, la, la, la, la, la, ala 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. A trisomy means the presence of three (instead of the normal two) chromosomes of a particular numbered type in an organism. ... In biology, meiosis is the process that allows one diploid cell to divide in a special way to generate haploid cells in eukaryotes. ... In biology, nondisjunction is the failure of a chromosome to split correctly during meiosis. ... Individuals in the mollusk species Donax variabilis show diverse coloration and patterning in their phenotypes. ...


Sometimes intersex conditions can be caused by mosaicism - where some cells in the body have XX and others XY chromosomes. An intersexual is a person (or individual of any unisexual species) who is born with genitalia and/or secondary sexual characteristics of indeterminate sex, or which combine features of both sexes. ... A sex-determination system is a biological system that determines the development of sexual characteristics in an organism. ...


Another example of a mosaic genotype is one of the milder forms of Klinefelter's 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. The genotype is the specific genetic makeup (the specific genome) of an individual, in the form of DNA. Together with the environmental variation that influences the individual, it codes for the phenotype of that individual. ... ...


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. A genetic disorder, or genetic disease is a disease caused, at least in part, by the genes of the person with the disease. ... This article or section does not cite its references or sources. ...


Use in experimental biology

Genetic mosaics can be extraordinarily useful in the study of biological systems, and can be created intentionally in many model organisms in a variety of ways. They often allow for the study of genes that are important for very early events in development, making it otherwise difficult to obtain adult organisms in which later effects would be apparent. Furthermore they can be used to determine the tissue or cell type in which a given gene is required and to determine whether a gene is cell autonomous. That is whether the gene acts solely within the cell that is expressing it or whether it affects neighboring cells which do not themselves show a phenotype when carrying a mutation in the gene. A model organism is one that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workings of other organisms. ...


The earliest examples of this involved transplantation experiments (technically creating chimeras) where cells from a blastula stage embryo from one genetic background are aspirated out and injected into a blastula stage embryo of a different genetic background. Blastulation. ...


Genetic mosaics are a particularly powerful tool when used in the commonly studied fruit fly, Drosophila melanogaster where they are created through mitotic recombination. Mosaics were originally created by irradiating flies heterozygous for a particular allele with X-rays, inducing double-strand DNA breaks which, when repaired, could result in a cell homozygous for one of the two alleles. After further rounds of replication, this cell would result in a patch, or "clone" of cells mutant for the allele being studied. Binomial name Drosophila melanogaster Meigen, 1830 Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a dipteran (two-winged) insect, and is the species of fruit fly that is most commonly used in genetic experiments; it is among the most important model organisms. ...


More recently the use of a transgene incorporated into the Drosophila genome has made the system far more flexible. The Flip Recombinase (or FLP) is a gene from the commonly studied yeast Saccharomyces cerevisiae which recognizes "Flip Recombinase Target" sites, which are short sequences of DNA, and induces recombination between them. FRT sites have been inserted transgenically near the centromere of each chromosome arm of Drosophila melanogaster. The FLP gene can then be induced selectively, commonly using either the heat shock promoter or the GAL4/UAS system. The resulting clones can be identified either negatively or positively. A transgene is a gene or genetic material which has been transferred by any of a number of genetic engineering techniques from one organism to another. ... Binomial name Saccharomyces cerevisiae Meyen ex E.C. Hansen Saccharomyces cerevisiae is a species of budding yeast. ... Recombination usually refers to the biological process of genetic recombination and meiosis, a genetic event that occurs during the formation of sperm and egg cells. ... The centromere is a region of chromosomes with a special sequence and structure. ... Binomial name Drosophila melanogaster Meigen, 1830 Drosophila melanogaster (from the Greek for black-bellied dew-lover) is a dipteran (two-winged) insect, and is the species of fruit fly that is most commonly used in genetic experiments; it is among the most important model organisms. ...


In negatively marked clones the fly is transheterozygous for a gene encoding a visible marker (commonly the green fluorescent protein, GFP) and an allele of a gene to be studied (both on chromosomes bearing FRT sites). After induction of FLP expression, cells that undergo recombination will have progeny that are homozygous for either the marker or the allele being studied. Therefore the cells that do not carry the marker (which are dark) can be identified as carrying a mutation. Fluorescence induced by exposure to ultraviolet light in vials containing various sized cadmium selenide (CdSe) quantum dots. ... GFP ribbon diagram from PDB database The green fluorescent protein (GFP) is a protein from the jellyfish Aequorea victoria that fluoresces green when exposed to blue light. ...


It is sometimes inconvenient to use negatively marked clones, especially when generating very small patches of cells, where it is more difficult to see a dark spot on a bright background than a bright spot on a dark background. It is possible to create positively marked clones using the so called MARCM (pronounced mark-em) system, which stands for "Mosaic Analysis with a Repressible Cell Marker" and was developed by Liqun Luo, a professor at Stanford University. In this system the GAL4/UAS system is used to globally express GFP. However the gene GAL80 is used to repress the action of GAL4, preventing the expression of GFP. Instead of using GFP to mark the wild type chromosome as above, GAL80 serves this purpose, so that when it is removed, GAL4 is allowed to function, and GFP turns on. This results in the cells of interest being marked brightly in a dark background. Stanford redirects here. ...


  Results from FactBites:
 
Mosaic (genetics) - Wikipedia, the free encyclopedia (943 words)
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.
Genetic mosaics can be extraordinarily useful in the study of biological systems, and can be created intentionally in many model organisms in a variety of ways.
Mosaics were originally created by irradiating flies heterozygous for a particular allele with X-rays, inducing double-strand DNA breaks which, when repaired, could result in a cell homozygous for one of the two alleles.
Genetic mosaics (2996 words)
Mosaic animals can then be used to ask whether or not the cellular focus of action with respect to this phenotype is in the very cell or cells that exhibit the abnormality; this is equivalent to asking whether or not the gene acts cell autonomously with respect to the cellular phenotype.
Worm genetic mosaics have usually been generated from zygotes that were homozygous mutant for the gene under study and carried the wild-type allele of the same gene on an extrachromosomal element—either an extrachromosomal array or a free duplication of part of a chromosome—that was subject to spontaneous mitotic loss.
Mosaics, such as the example in A, that have not inherited the array in the intestine (fl nuclei), are resistant to the Bacillus thuringiensis toxin, indicating that bre-5 is required in the intestine for susceptibility (Griffitts et al., 2001).
  More results at FactBites »

 
 

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