Editing Chimera (genetics) (section)

==Classifications==

===Natural chimerism===
{{Needs expansion|date=October 2024}}
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. 

==== Sponges ====
Chimerism has been found in some species of marine sponges.<ref name="Blanquer,A" /> Four distinct genotypes have been found in a single individual, and there is potential for even greater genetic heterogeneity. Each genotype functions independently in terms of reproduction, but the different intra-organism genotypes behave as a single large individual in terms of ecological responses like growth.<ref name="Blanquer,A" />

==== In obligates ====
{{See also|Yellow crazy ant#Reproduction}}

It has been shown that male [[yellow crazy ant]]s are obligate chimeras, the first known such case. In this species, the queens have arisen from fertilized eggs with a genotype of RR (Reproductive × Reproductive), the sterile female workers show a RW arrangement (Reproductive × Worker), and the males instead of being haploid, as is usually the case for ants, also display a RW genotype, but for them the egg R and the sperm W do not fuse so they develop as a chimera with some cells carrying an R and others carrying a W genome.<ref>{{Cite journal |last1=Darras |first1=H. |last2=Berney |first2=C. |last3=Hasin |first3=S. |last4=Drescher |first4=J. |last5=Feldhaar |first5=H. |last6=Keller |first6=L. |date=2023-04-07 |title=Obligate chimerism in male yellow crazy ants |url=http://dx.doi.org/10.1126/science.adf0419 |journal=Science |volume=380 |issue=6640 |pages=55–58 |doi=10.1126/science.adf0419 |pmid=37023182 |bibcode=2023Sci...380...55D |s2cid=257985666 |issn=0036-8075}}</ref><ref>{{Cite journal |last=Callaway |first=Ewen |date=2023-04-06 |title=Crazy ants' strange genomes are a biological first |url=https://www.nature.com/articles/d41586-023-01002-3 |journal=Nature |language=en |doi=10.1038/d41586-023-01002-3|pmid=37024590 |s2cid=258007429 }}</ref>

===Artificial chimerism ===
[[File:Backcrossing mice from chimera edit.svg|right|thumb|upright|Chimeric trait distribution by generation]]

Artificial chimerism refers to examples of chimerism that are accidentally produced by humans, either for research or commercial purposes. 

====Tetragametic chimerism====
[[File:African violet chimeras.jpg|right|thumb|upright=1|African violets exhibiting chimerism]]

Tetragametic chimerism is a form of congenital chimerism. This condition occurs through fertilizing two separate ova by two sperm, followed by aggregation of the two at the [[blastocyst]] or zygote stages. This results in the development of an organism with intermingled cell lines. Put another way, the chimera is formed from the merging of two [[twin|nonidentical twins]]. As such, they can be male, female, or intersex. <ref>{{Cite journal |last1=Schoenle |first1=E. |last2=Schmid |first2=W. |last3=Schinzel |first3=A. |last4=Mahler |first4=M. |last5=Ritter |first5=M. |last6=Schenker |first6=T.|last7=Metaxas |first7=M. |last8=Froesch |first8=P. |last9=Froesch |first9=E. R. |date=1983-07-01 |title=46,XX/46,XY chimerism in a phenotypically normal man |journal=Human Genetics |language=en |volume=64 |issue=1 |pages=86–89 |doi=10.1007/BF00289485 |pmid=6575956 |s2cid=25946104 |issn=1432-1203|url=https://www.zora.uzh.ch/id/eprint/228692/1/BF00289485.pdf }}</ref><ref>{{Cite journal |last1=Binkhorst |first1=Mathijs |last2=de Leeuw |first2=Nicole |last3=Otten |first3=Barto J. |date=January 2009 |title=A healthy, female chimera with 46,XX/46,XY karyotype |journal=Journal of Pediatric Endocrinology & Metabolism |volume=22 |issue=1 |pages=97–102 |doi=10.1515/jpem.2009.22.1.97 |issn=0334-018X |pmid=19344081 |s2cid=6074854}}</ref><ref>{{Cite journal |last1=Gencík |first1=A. |last2=Genciková |first2=A. |last3=Hrubisko |first3=M. |last4=Mergancová |first4=O. |date=1980 |title=Chimerism 46,XX/46,XY in a phenotypic female |journal=Human Genetics |volume=55 |issue=3 |pages=407–408 |doi=10.1007/bf00290226 |issn=0340-6717 |pmid=7203474|s2cid=9117759}}</ref><ref>{{Cite journal |last1=Farag |first1=T I |last2=Al-Awadi |first2=S A |last3=Tippett |first3=P |last4=el-Sayed |first4=M |last5=Sundareshan |first5=T S |last6=Al-Othman |first6=S A |last7=el-Badramany |first7=M H |date=December 1987 |title=Unilateral true hermaphrodite with 46,XX/46,XY dispermic chimerism. |journal=Journal of Medical Genetics |volume=24 |issue=12 |pages=784–786 |issn=0022-2593 |pmc=1050410 |pmid=3430558 |doi=10.1136/jmg.24.12.784}}</ref><ref>{{Cite journal |last1=Shah |first1=V. C. |last2=Krishna Murthy |first2=D. S. |last3=Roy |first3=S. |last4=Contractor |first4=P. M. |last5=Shah |first5=A. V. |date=November 1982 |title=True hermaphrodite: 46, XX/46, XY, clinical cytogenetic and histopathological studies |journal=Indian Journal of Pediatrics |volume=49 |issue=401 |pages=885–890 |doi=10.1007/bf02976984 |issn=0019-5456 |pmid=7182365 |s2cid=41204037}}</ref><ref name="Strain" /><ref>{{Cite journal |last1=Hadjiathanasiou |first1=C. G. |last2=Brauner |first2=R. |last3=Lortat-Jacob |first3=S. |last4=Nivot |first4=S. |last5=Jaubert |first5=F. |last6=Fellous |first6=M. |last7=Nihoul-Fékété |first7=C. |last8=Rappaport |first8=R. |date=November 1994 |title=True hermaphroditism: genetic variants and clinical management |journal=The Journal of Pediatrics |volume=125 |issue=5 Pt 1 |pages=738–744 |doi=10.1016/s0022-3476(94)70067-2 |issn=0022-3476 |pmid=7965425}}</ref>{{citation overkill|date=May 2022}}

The tetragametic state has important implications for organ or [[stem cell]] transplantation. Chimeras typically have [[immunologic tolerance]] to both cell lines.{{Citation needed|date=January 2017}}

====Microchimerism====
{{Main| Microchimerism}}

Microchimerism is the presence of a small number of cells that are genetically distinct from those of the host individual. Most people are born with a few cells genetically identical to their mothers' and the proportion of these cells goes down in healthy individuals as they get older. 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.

The higher rates of autoimmune diseases due to the presence of maternally-derived cells is why in a 2010 study of a 40-year-old man with scleroderma-like disease (an autoimmune rheumatic disease), the female cells detected in his blood stream via FISH (fluorescence in situ hybridization) were thought to be maternally-derived. However, his form of microchimerism was found to be due to a vanished twin, and it is unknown whether microchimerism from a vanished twin might predispose individuals to autoimmune diseases as well.<ref>{{cite journal |last1=Bellefon |first1=L. |last2=Heiman |first2=P. |last3=Kanaan |first3=S. |last4=Azzouz |first4=D. |last5=Rak |first5=J. |last6=Martin |first6=M. |last7=Roudier |first7=J. |last8=Roufosse |first8=F. |last9=Lambert |first9=C. |year=2010 |title=Cells from a vanished twin as a source of microchimerism 40 years later |journal=Chimerism |volume=1 |issue=2 |pages=56–60 |doi=10.4161/chim.1.2.14294 |pmid=21327048 |pmc=3023624}}</ref> Mothers often also have a few cells genetically identical to those of their children, and some people also have some cells genetically identical to those of their siblings (maternal siblings only, since these cells are passed to them because their mother retained them).{{Citation needed|date=January 2017}}

====Germline chimerism====
Germline chimerism occurs when the germ cells (for example, [[sperm]] and [[ovum|egg]] cells) of an organism are not genetically identical to its own. It has been recently discovered that [[marmoset]]s can carry the reproductive cells of their (fraternal) twin siblings due to placental fusion during development. (Marmosets almost always give birth to fraternal twins.)<ref name="Ross2007" /><ref>{{cite news | url=https://www.nytimes.com/2007/03/27/science/27marm.html | work=The New York Times | title=In the Marmoset Family, Things Really Do Appear to Be All Relative | first=Carl | last=Zimmer | date=2007-03-27 | access-date=2010-04-01}}</ref><ref>{{cite news | url=https://www.newscientist.com/article/dn11464-marmosets-may-carry-their-siblings-sex-cells.html| title=Marmosets may carry their sibling's sex cells| last=Hooper| first=Rowan| date=26 March 2007| work=[[New Scientist]]}}</ref>