Introduction On rare occasions, a coat colouring can grab the attention of the gerbil community and usually these coats with their unusual markings involve mosaicism or chimerism. These animals are usually bi-coloured or tri-coloured when combined with Spotting.
Somatic mosaicism[ edit ] Somatic mosaicism occurs when the somatic cells of the body are of more than one genotype. In the more common mosaics, different genotypes arise from a single fertilized egg cell, due to mitotic errors at first or later cleavages. Although most forms of trisomy are due to problems in meiosis and affect all cells of the organism, there are cases where the trisomy occurs in only a selection of the cells.
This may be caused by a nondisjunction event in an early mitosis, resulting in a loss of a chromosome from some trisomic cells. But mosaicism need not necessarily be deleterious. Revertant somatic mosaicism is a rare recombination event in which there is a spontaneous correction of a mutant, pathogenic allele.
The latter is the case in normal XX female mammals, although it is not always visible from the phenotype like it is in calico cats. However, all multicellular organisms are likely to be somatic mosaics to some extent.
As our longevity has increased dramatically over the last century, our genome may not have had time to adapt to cumulative effects of mutagenesis. It was first discovered by Chimera mosaicism Stern in Drosophila in The amount of tissue which is mosaic depends Chimera mosaicism where in the tree of cell division the Chimera mosaicism takes place.
A phenotypic character called "Twin Spot" seen in Drosophila is a result of mitotic recombination. However, it also depends on the allelic status of the genes undergoing recombination. Twin spot occurs only if the heterozygous genes are linked in repulsion i. The recombination needs to occur between the centromere the adjacent gene.
This gives an appearance of yellow patches on the wild type background in Drosophila. The resulting BLM protein is defective. Germline mosaicism Germline or gonadal mosaicism is a special form of mosaicism, where some gametes —i.
This can cause only some offspring to be affected, even for a dominant disease.
Use in experimental biology[ edit ] 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 or not the gene acts solely within the cell of that genotype, or if it affects the entire organism of neighboring cells which do not themselves contain that genotype.
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.
Genetic mosaics are a particularly powerful tool when used in the commonly studied fruit flywhere specially-selected strains frequently lose an X  or a Y  chromosome in one of the first embryonic cell divisions.
These mosaics can then be used to analyze such things as courtship behavior,  female sexual attraction,  and the autonomy or non-autonomy of particular genes. Genetic mosaics can also be created through mitotic recombination.
Such mosaics were originally created by irradiating flies heterozygous for a particular allele with X-raysinducing 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.
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" FRT 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 resulting clones can be identified either negatively or positively.
In negatively marked clones the fly is transheterozygous for a gene encoding a visible marker commonly the green fluorescent protein or 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. 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 "mosaic analysis with a repressible cell marker", pronounced [mark-em] system, developed by Liqun Luoa professor at Stanford Universityand his post-doc Tzumin Lee who now leads a group at Janelia Farm Research Campus.
This results in the cells of interest being marked brightly in a dark background. These are organisms which contain two or more genetically distinct types of tissue. Cotterman in in his seminal paper on antigenic variation.Mosaic (genetics) Jump to navigation Jump to search.
This girl has one brown eye and one hazel/green eye Cat with different coloured eyes. In genetics, a mosaic (or mosaicism) means the presence of two different genotypes in an individual which developed from a single fertilized egg. As a result, A genetic chimera is an organism.
Mosaicism, Chimerism and X-Inactivation. The charges against her were eventually dismissed when it was proven that she was a chimera and matching DNA was found in her cervical tissue.
Mosaicism or chimerism shouldn’t be confused with X-inactivation. This occurs when all the cells in an organism have the same genotype, but a different. 46,XX/46,XY is a chimeric genetic disorder caused by having two distinct cell populations within the body. The chimerism arises in utero from the combination of an XX zygote and an XY zygote (which otherwise would have developed into twins) into a single embryo.
It is not to be confused with mosaicism and hybridism. 46,XX/46,XY is typically associated with Intersex conditions such as ambiguous. “It’s a fairly straightforward example of X-inactivation mosaicism, with the addition of a white spotting gene.
All female mammals have two X-chromosomes,” explained the professor. In genetics, a chimera is an individual with 2 or more distinct, unrelated genetic lineages (ie, 46XX/46XX, 46XX/46XY, or 46XY/46XY). This condition is not to be confused with germline mosaicism, in which a mutation occurs during mitosis, altering part of a genetic line (aneuploidy).
5: any of numerous virus diseases of plants characterized by diffuse light and dark green or yellow and green mottling of the foliage — compare tobacco mosaic virus.