Chimera (genetics)
A genetic chimerism or chimera (/kaɪˈmɪərə/ ky-MEER-ə or /kɪˈmɪərə/ kim-EER-ə) is a single organism composed of cells with more than one distinct genotype.
In plants and some animal chimeras, mosaicism involves distinct types of tissue that originated from the same zygote but differ due to mutation during ordinary cell division.
[2] In contrast, an individual where each cell contains genetic material from two organisms of different breeds, varieties, species or genera is called a hybrid.
[3] Another way that chimerism can occur in animals is by organ transplantation, giving one individual tissues that developed from a different genome.
[4] Some level of chimerism occurs naturally in the wild in many animal species, and in some cases may be a required (obligate) part of their life cycle.
Once fused to a female, the males will reach sexual maturity, developing large testicles as their other organs atrophy.
This process allows for sperm to be in constant supply when the female produces an egg, so that the chimeric fish is able to have a greater number of offspring.
[9][10][11][12][13][14][15][excessive citations] The tetragametic state has important implications for organ or stem cell transplantation.
[citation needed] Microchimerism is the presence of a small number of cells that are genetically distinct from those of the host individual.
People who retain higher numbers of cells genetically identical to their mother's have been observed to have higher rates of some autoimmune diseases, presumably because the immune system is responsible for destroying these cells and a common immune defect prevents it from doing so and also causes autoimmune problems.
It has been recently discovered that marmosets can carry the reproductive cells of their (fraternal) twin siblings due to placental fusion during development.
[28] In artificial chimerism, an individual has one cell lineage that was inherited genetically at the time of the formation of the human embryo and the other that was introduced through a procedure, including organ transplantation or blood transfusion.
[30] In contrast, a human where each cell contains genetic material from two organisms of different breeds, varieties, species or genera is called a human–animal hybrid.
[32] This condition is either innate or it is synthetic, acquired for example through the infusion of allogeneic blood cells during transplantation or transfusion.
[citation needed] In nonidentical twins, innate chimerism occurs by means of blood vessel anastomoses.
[citation needed] On January 22, 2019, the National Society of Genetic Counselors released an article Chimerism Explained: How One Person Can Unknowingly Have Two Sets of DNA, where they state, "where a twin pregnancy evolves into one child, is currently believed to be one of the rarer forms.
[36][37] Periclinal chimeras involve a genetic difference that persists in the descendant cells of a particular meristem layer.
[39] Just as the constituent species are likely to differ in a wide range of features, so the behavior of their periclinal chimeras is like to be highly variable.
Reporter genes such as GUS and Green Fluorescent Protein[45] (GFP) are used in combination with plant selective markers (herbicide, antibody etc.).
However, GUS expression depends on the plant development stage and GFP may be influenced by the green tissue autofluorescence.
[46] In 2012, the first example of a naturally-occurring RNA-DNA hybrid virus was unexpectedly discovered during a metagenomic study of the acidic extreme environment of Boiling Springs Lake that is in Lassen Volcanic National Park, California.
[22] A major milestone in chimera experimentation occurred in 1984 when a chimeric sheep–goat was produced by combining embryos from a goat and a sheep, and survived to adulthood.
[53] Once hatched, the quail feathers were visibly apparent around the wing area, whereas the rest of the chick's body was made of its own chicken cells.
The embryos were allowed to develop for several days in a laboratory setting, and then destroyed to harvest the resulting stem cells.
The general methods for creating chimeric mice can be summarized either by injection or aggregation of embryonic cells from different origins.
Since this discovery occurred in 1988, ES cells have become a key tool in the generation of specific chimeric mice.
Between the stages of fertilization of the egg and the implantation of a blastocyst into the uterus, different parts of the mouse embryo retain the ability to give rise to a variety of cell lineages.
Once the embryo has reached the blastocyst stage, it is composed of several parts, mainly the trophectoderm, the inner cell mass, and the primitive endoderm.
In the case where two diploid eight-cell-stage embryos are used to make a chimera, chimerism can be later found in the epiblast, primitive endoderm, and trophectoderm of the mouse blastocyst.
[70] The US and Western Europe have strict codes of ethics and regulations in place that expressly forbid certain subsets of experimentation using human cells, though there is a vast difference in the regulatory framework.
