Editing Chimera (genetics) (section)

===Animals===

As the organism develops, it can come to possess [[organ (anatomy)|organ]]s that have different sets of [[chromosome]]s. For example, the chimera may have a [[liver]] composed of cells with one set of chromosomes and have a [[kidney]] composed of cells with a second set of chromosomes. This has occurred in humans, and at one time was thought to be extremely rare although more recent evidence suggests that this is not the case.<ref name="Norton" /><ref>Boklage, C.E. How New Humans Are Made. Hackensack, NJ; London: World Scientific Publishing Co. Pte. Ltd; 2010</ref>

This is particularly true for the [[marmoset]]. Recent research shows most marmosets are chimeras, sharing DNA with their [[fraternal twin]]s.<ref name="Ross2007" /> 95% of marmoset fraternal twins trade blood through [[chorionic]] fusions, making them [[hematopoietic]] chimeras.<ref name="Masahito Tachibana, Michelle Sparman and Shoukhrat Mitalipov" /><ref>{{cite journal | first1=N.| last1=Gengozian| last2=Batson| first2=JS| first3=P.| last3=Eide| title=Hematologic and Cytogenetic Evidence for Hematopoietic Chimerism in the Marmoset, Tamarinus Nigricollis| journal=Cytogenetics| year=1964| volume=10| issue=6| pages=384–393| doi=10.1159/000129828| pmid=14267132}}</ref>

In the [[budgerigar]], due to the many existing [[budgerigar colour genetics|plumage colour variations]], tetragametic chimeras can be very conspicuous, as the resulting bird will have an obvious split between two colour types{{snd}} often divided bilaterally down the centre. These individuals are known as [[half-sider budgerigar]]s.<ref name="guardian">{{cite news |last1=GrrlScientist |title=Half-siders: A tale of two birdies |url=https://www.theguardian.com/science/grrlscientist/2014/jan/31/grrlscientist-halfsider-chimera-bilateral-gynandromorph-birds |website=The Guardian |access-date=30 July 2023}}</ref>

An animal chimera is a single [[organism]] that is composed of two or more different populations of genetically distinct [[cell (biology)|cells]] that originated from different [[zygote]]s involved in [[sexual reproduction]]. If the different cells have emerged from the same zygote, the organism is called a [[Mosaic (genetics)|mosaic]]. Innate chimeras are formed from at least four parent cells (two fertilised eggs or early embryos fused together). Each population of cells keeps its own character and the resulting organism is a mixture of tissues. Cases of [[human chimera]]s have been documented.<ref name="Norton" />

====Chimerism in humans====
{{Main|Human chimera}}Some consider [[Mosaic (genetics)|mosaicism]] to be a form of chimerism,<ref>{{Cite web |title=Chimaera - an overview |website=ScienceDirect |url=https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/chimaera |access-date=2024-01-20 |quote=Another form of chimera is the mosaic, which is a composite individual derived from a single fertilized egg.}}</ref> while others consider them to be distinct.<ref>{{Cite journal |last=Madan |first=Kamlesh |date=2020-09-01 |title=Natural human chimeras: A review |journal=European Journal of Medical Genetics |volume=63 |issue=9 |pages=103971 |doi=10.1016/j.ejmg.2020.103971 |issn=1769-7212 |quote=A chimera is an organism whose cells are derived from two or more zygotes as opposed to a mosaic whose different cell lines are derived from a single zygote|doi-access=free |pmid=32565253 }}</ref><ref>{{Cite journal |last1=Anderson |first1=D. |last2=Billingham |first2=R. E. |last3=Lampkin |first3=G. H. |last4=Medawar |first4=P. B. |date=1951-12-01 |title=The use of skin grafting to distinguish between monozygotic and dizygotic twins in cattle |url=https://www.nature.com/articles/hdy195138 |journal=Heredity |language=en |volume=5 |issue=3 |pages=379–397 |doi=10.1038/hdy.1951.38 |issn=1365-2540 |quote=In the current embryological (which is also the classical) sense, a 'chimaera' is an organism whose cells derive from two or more distinct zygote lineages, and this is the sense which the term 'genetical chimaera' is here intended to convey. 'Genetical mosaic' is less suitable, because a mosaic is formed of the cells of a single zygote lineage.}}</ref><ref name=":0">{{Cite journal |last=Santelices |first=B. |date=2004-11-01 |title=Mosaicism and chimerism as components of intraorganismal genetic heterogeneity |url=https://academic.oup.com/jeb/article/17/6/1187/7323396 |journal=Journal of Evolutionary Biology |language=en |volume=17 |issue=6 |pages=1187–1188 |doi=10.1111/j.1420-9101.2004.00813.x |pmid=15525401 |issn=1010-061X |quote=Mosaicism originates by intrinsic genetic variations caused, among other processes, by somatic mutations, while chimerism originates from allogenic fusion or grafting. As such, chimerism is much rarer and involves a much larger genetic change than mosaicism.}}</ref> Mosaicism involves a [[mutation]] of the genetic material in a cell, giving rise to a subset of cells that are different from the rest. Natural chimerism is the fusion of more than one fertilized [[zygote]] in the early stages of [[prenatal development]]. It is much rarer than mosaicism.<ref name=":0" />

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]].<ref>{{Cite journal |last=Rinkevich |first=B. |date=June 2001 |title=Human natural chimerism: an acquired character or a vestige of evolution? |journal=Human Immunology |volume=62 |issue=6 |pages=651–657 |doi=10.1016/s0198-8859(01)00249-x |issn=0198-8859 |pmid=11390041}}</ref> Specific types of transplants that could induce this condition include bone marrow transplants and organ transplants, as the recipient's body essentially works to permanently incorporate the new blood stem cells into it.

Boklage argues that many human 'mosaic' cell lines will be "found to be chimeric if properly tested".<ref>{{Cite journal |last=Boklage |first=Charles E. |date=2006 |title=Embryogenesis of chimeras, twins and anterior midline asymmetries |url=https://academic.oup.com/humrep/article/21/3/579/770117 |journal=Human Reproduction |volume=21 |issue=3 |pages=579–591 |doi=10.1093/humrep/dei370 |doi-access=free|pmid=16253966 }}</ref>

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]].<ref>{{cite web |url=https://embryo.asu.edu/pages/hybrids-and-chimeras-consultation-ethical-and-social-implications-creating-humananimal-embryos |title='Hybrids and Chimeras: A Consultation on the Ethical and Social Implications of Creating Human/Animal Embryos in Research' (2007), by the HFEA |website=The Embryo Project at Arizona State University |first1=Sarah |last1=Taddeo |first2=Jason S. |last2=Robert |date=2014-11-04}}</ref>

While German [[dermatologist]] [[Alfred Blaschko]] described [[Blaschko's lines]] in 1901, the genetic science took until the 1930s to approach a vocabulary for the phenomenon. The term ''genetic chimera'' has been used at least since the 1944 article of Belgovskii.<ref name="belgovskii44">{{cite book |last1=Belgovskii |first1=M. L. |title=OTS 61-11476 |date=1944 |publisher=United States Department of Commerce Office of Technical Services |chapter=The Causes of Mosaicism Associated With Heterochromatic Chromosome Regions}}</ref>

This condition is either innate or it is synthetic, acquired for example through the infusion of [[allogeneic]] [[blood cell]]s during [[Organ transplant|transplantation]] or [[Blood transfusion|transfusion]].{{citation needed|date=February 2021}}

In nonidentical twins, innate chimerism occurs by means of blood vessel [[anastomose]]s. The likelihood of offspring being a chimera is increased if it is created via [[in vitro fertilization|in vitro fertilisation]].<ref name="Strain" /> Chimeras can often breed, but the fertility and type of offspring depend on which cell line gave rise to the ovaries or testes; varying degrees of [[intersex]] differences may result if one set of cells is genetically female and another genetically male.{{citation needed|date=February 2021}}

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. However, we know that 20 to 30% of singleton pregnancies were originally a twin or a multiple pregnancy".<ref>{{Cite web|url=https://www.nsgc.org/p/bl/et/blogaid=1084|title=Chimerism Explained: How One Person Can Unknowingly Have Two Sets of DNA|website=National Society of Genetic Counselors|access-date=2020-02-02|archive-date=2020-02-02 |archive-url=https://web.archive.org/web/20200202124939/https://www.nsgc.org/p/bl/et/blogaid%3D1084|url-status=dead}}</ref>

Most human chimeras will go through life without realizing they are chimeras. The difference in phenotypes may be subtle (e.g., having a [[hitchhiker's thumb]] and a straight thumb, eyes of slightly different colors, differential hair growth on opposite sides of the body, etc.) or completely undetectable. Chimeras may also show, under a certain spectrum of UV light, distinctive marks on the back resembling that of arrow points pointing downward from the shoulders down to the lower back; this is one expression of pigment unevenness called [[Blaschko's lines]].<ref>{{cite web |url=http://www.thetech.org/genetics/ask.php?id=75 |title=Understanding Genetics: Human Health and the Genome |date=November 30, 2004 |work=Ask a Geneticist |publisher=[[Stanford University School of Medicine]] |first1=Barry |last1=Starr |archive-url=https://web.archive.org/web/20110724035334/http://www.thetech.org/genetics/ask.php?id=75 |archive-date=2011-07-24}}<!-- Date determined from list at https://web.archive.org/web/20110805030220/http://www.thetech.org/genetics/asklist.php?category=% --></ref>

{{anchor|(KarenKeegan)}}Another case was that of Karen Keegan, who was also suspected (initially) of not being her children's biological mother, after DNA tests on her adult sons for a kidney transplant she needed seemed to show that she was not their mother.<ref name="Norton" /><ref>{{cite episode |url=http://www.five.tv/programmes/extraordinarypeople/twininside/ |title=The Twin Inside Me: Extraordinary People |series=Extraordinary People |station=[[Five (TV channel)|Channel 5]] (UK) |date=9 March 2006 |archive-url=https://web.archive.org/web/20060526105634/http://www.five.tv/programmes/extraordinarypeople/twininside/ |archive-date=May 26, 2006 |url-status=dead}}</ref>