Editing Barr body (section)

== History ==

=== 1928 - Foundational Research ===
The discovery of the Barr body was based on the research of geneticist [[Emil Heitz]] studying the dynamics of moss chromatin during mitosis.<ref name=":10">{{Cite journal |last1=Galupa |first1=Rafael |last2=Heard |first2=Edith |date=2018-11-23 |title=X-Chromosome Inactivation: A Crossroads Between Chromosome Architecture and Gene Regulation |url=https://www.annualreviews.org/content/journals/10.1146/annurev-genet-120116-024611 |journal=Annual Review of Genetics |language=en |volume=52 |issue= |pages=535–566 |doi=10.1146/annurev-genet-120116-024611 |pmid=30256677 |issn=0066-4197}}</ref> Heitz distinguished between heterochromatin and [[euchromatin]], noting that certain regions of some chromosomes (and in some instances, entire chromosomes) retained their staining following mitosis.<ref name=":10" /> This retained staining is indicative of condensed chromatin which he hypothesized, in the absence of mitosis, reflects silent regions of chromosomes (heterochromatin).<ref name=":10" />

=== 1949 - Discovery of the Barr Body ===
Barr bodies were first discovered in 1949 by Canadian researcher [[Murray Barr]] and his undergraduate student Ewart Bertram.<ref name=":6">{{Cite journal |last=Miller |first=Fiona Alice |date=2006-09-01 |title='Your true and proper gender': the Barr body as a good enough science of sex |url=https://www.sciencedirect.com/science/article/abs/pii/S1369848606000446 |journal=Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences |volume=37 |issue=3 |pages=459–483 |doi=10.1016/j.shpsc.2006.06.010 |pmid=16980188 |issn=1369-8486}}</ref> While examining the [[Neural cell adhesion molecule|neuronal cells]] of female cats, they observed a distinct, densely staining structure that was absent in male cells.<ref name=":6" /> This structure was initially referred to as a "nucleolar satellite."<ref name=":6" /> Although its significance was not immediately understood, the observation laid the foundation for subsequent research in [[cytogenetics]].<ref name=":6" />

=== 1955 - Development of the Buccal Smear Test ===
In 1955, Barr, in collaboration with [[Keith L. Moore|K.L. Moore]], developed the [[Buccal smear|buccal smear test]], a non-invasive method for collecting epithelial cells from the inner lining of the mouth.<ref name=":7">{{Cite web |title=Buccal smear - illustration: MedlinePlus Medical Encyclopedia Image |url=https://medlineplus.gov/ency/imagepages/9140.htm#:~:text=A%20buccal%20smear%20is%20a,a%20normal%20female%20sex%20chromosome). |access-date=2025-04-04 |website=medlineplus.gov |language=en}}</ref> This technique allowed the detection of Barr bodies in somatic cells and provided a simple tool for identifying chromosomal abnormalities, such as those seen in Turner syndrome and Klinefelter syndrome. The test became widely used in the mid-20th century and was among the earliest tools for determining chromosomal sex in clinical and research contexts.<ref name=":7" />

=== 1959 - Identification of the Inactivated X Chromosome ===
In 1959, Japanese geneticist [[Susumu Ohno]] demonstrated that the previously identified "nucleolar satellite" was in fact the inactivated X chromosome in female somatic cells.<ref name=":8">{{Cite journal |last=Miller |first=Fiona Alice |date=2006-09-01 |title='Your true and proper gender': the Barr body as a good enough science of sex |url=https://www.sciencedirect.com/science/article/abs/pii/S1369848606000446 |journal=Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences |volume=37 |issue=3 |pages=459–483 |doi=10.1016/j.shpsc.2006.06.010 |pmid=16980188 |issn=1369-8486}}</ref> Using chromosomal staining techniques in animal models, such as rodents, he confirmed its identity and named it the "Barr body" in recognition of Barr's earlier discovery.<ref name=":8" /> Ohno's work clarified that the Barr body was not merely a structural feature but represented the functional silencing of one X chromosome.<ref name=":8" />

=== 1961 - Discovery of Lyonization ===
In 1961, British geneticist [[Mary Lyon (geneticist)|Mary Lyon]] proposed the concept of X chromosome inactivation, now known as [[Lyonization]].<ref name=":8" /> Her hypothesis suggested that in females, one of the two X chromosomes is randomly inactivated during early embryonic development to balance gene dosage.<ref name=":9">{{Cite journal |last=Lyon |first=Mary |date=22 April 1961 |title=Gene Action in the X-chromosome of the Mouse (Mus musculus L.) |journal=Nature |volume=190 |issue=4773 |pages=372–373|doi=10.1038/190372a0 |pmid=13764598 |bibcode=1961Natur.190..372L }}</ref> This idea was based on her observations of genetic [[Mosaic (genetics)|mosaicism]] in coat color patterns in mice.<ref name=":9" /> Lyon's work provided a mechanistic explanation for the presence of the Barr body, linking it directly to the process of X inactivation.<ref name=":8" />