Chromosome 21 is one of the 23 pairs of chromosomes in humans. Chromosome 21 is both the smallest human autosome and chromosome,[4] with 46.7 million base pairs (the building material of DNA) representing about 1.5 percent of the total DNA in cells. Most people have two copies of chromosome 21, while those with three copies of chromosome 21 (trisomy 21) have Down syndrome.
Researchers working on the Human Genome Project announced in May 2000 that they had determined the sequence of base pairs that make up this chromosome.[5] Chromosome 21 was the second human chromosome to be fully sequenced, after chromosome 22.
Genes
Number of genes
The following are some of the gene count estimates of human chromosome 21. Because researchers use different approaches to genome annotation, their predictions of the number of genes on each chromosome varies (for technical details, see gene prediction). Among various projects, the collaborative consensus coding sequence project (CCDS) takes an extremely conservative strategy. Thus CCDS's gene number prediction represents a lower bound on the total number of human protein-coding genes.[6]
Gene list
The following is a partial list of genes on human chromosome 21. For complete list, see the link in the infobox at the top of the article.
ABCG1: encoding ATP-binding cassette sub-family G member 1
ADAMTS1 encoding enzyme a disintegrin and metalloproteinase with thrombospondin motifs 1
ADAMTS5: encoding enzyme a disintegrin and metalloproteinase with thrombospondin motifs 5
The following conditions are caused by changes in the structure or number of copies of chromosome 21:
Cancers: Rearrangements (translocations) of genetic material between chromosome 21 and other chromosomes have been associated with several types of cancer. For example, acute lymphoblastic leukemia (a type of blood cancer most often diagnosed in childhood) has been associated with a translocation between chromosomes 12 and 21. Another form of leukemia, acute myeloid leukemia, has been associated with a translocation between chromosomes 8 and 21.
In a small percentage of cases, Down syndrome is caused by a rearrangement of chromosomal material between chromosome 21 and another chromosome. As a result, a person has the usual two copies of chromosome 21, plus extra material from chromosome 21 attached to another chromosome. These cases are called translocation Down syndrome. Researchers believe that extra copies of genes on chromosome 21 disrupt the course of normal development, causing the characteristic features of Down syndrome and the increased risk of medical problems associated with this disorder.
Other changes in the number or structure of chromosome 21 can have a variety of effects, including intellectual disability, delayed development, and characteristic facial features. In some cases, the signs and symptoms are similar to those of Down syndrome. Changes to chromosome 21 include a missing segment of the chromosome in each cell (partial monosomy 21) and a circular structure called ring chromosome 21. A ring chromosome occurs when both ends of a broken chromosome are reunited.
Duplication in amyloid precursor protein (APP) locus (duplicated segment varies in length but includes APP) on Chromosome 21 was found to cause early onset familial Alzheimer's disease in a French family set (Rovelet-Lecrux et al. 2005) and a Dutch family set.[13] Compared to Alzheimer's caused by missense mutations in APP, the frequency of the Alzheimer's caused by APP duplications is significant. All patients that have an extra copy of APP gene due to the locus duplication show Alzheimer's with severe cerebral amyloid angiopathy.
Cytogenetic band
G-banding ideograms of human chromosome 21
References
^ a b"Search results - 21[CHR] AND "Homo sapiens"[Organism] AND ("has ccds"[Properties] AND alive[prop]) - Gene". NCBI. CCDS Release 24 for Homo sapiens. 2022-10-26. Retrieved 2022-12-23.
^Tom Strachan; Andrew Read (2 April 2010). Human Molecular Genetics. Garland Science. p. 45. ISBN 978-1-136-84407-2.
^ a b cGenome Decoration Page, NCBI. Ideogram data for Homo sapience (850 bphs, Assembly GRCh38.p3). Last update 2014-06-03. Retrieved 2017-04-26.
^"Chromosome 21".
^Hattori, M.; Fujiyama, A.; Taylor, T. D.; Watanabe, H.; Yada, T.; Park, H.-S.; Toyoda, A.; Ishii, K.; Totoki, Y.; Choi, D.-K.; Soeda, E.; Ohki, M.; Takagi, T.; Sakaki, Y.; Taudien, S.; Blechschmidt, K.; Polley, A.; Menzel, U.; Delabar, J.; Kumpf, K.; Lehmann, R.; Patterson, D.; Reichwald, K.; Rump, A.; Schillhabel, M.; Schudy, A.; Zimmermann, W.; Rosenthal, A.; Kudoh, J.; et al. (2000). "The DNA sequence of human chromosome 21". Nature. 405 (6784): 311–319. Bibcode:2000Natur.405..311H. doi:10.1038/35012518. PMID 10830953.
^Pertea M, Salzberg SL (2010). "Between a chicken and a grape: estimating the number of human genes". Genome Biol. 11 (5): 206. doi:10.1186/gb-2010-11-5-206. PMC 2898077. PMID 20441615.
^"Statistics & Downloads for chromosome 21". HUGO Gene Nomenclature Committee. 2022-12-23. Archived from the original on 2017-06-29. Retrieved 2022-12-23.
^"Human chromosome 21: entries, gene names and cross-references to MIM". UniProt. 2018-02-28. Retrieved 2018-03-16.
^"Search results - 21[CHR] AND "Homo sapiens"[Organism] AND ("genetype protein coding"[Properties] AND alive[prop]) - Gene". NCBI. 2017-05-19. Retrieved 2017-05-20.
^"Search results - 21[CHR] AND "Homo sapiens"[Organism] AND ( ("genetype miscrna"[Properties] OR "genetype ncrna"[Properties] OR "genetype rrna"[Properties] OR "genetype trna"[Properties] OR "genetype scrna"[Properties] OR "genetype snrna"[Properties] OR "genetype snorna"[Properties]) NOT "genetype protein coding"[Properties] AND alive[prop]) - Gene". NCBI. 2017-05-19. Retrieved 2017-05-20.
^"Search results - 21[CHR] AND "Homo sapiens"[Organism] AND ("genetype pseudo"[Properties] AND alive[prop]) - Gene". NCBI. 2017-05-19. Retrieved 2017-05-20.
^ a b cSleegers K, Brouwers N, Gijselinck I, Theuns J, Goossens D, Wauters J, Del-Favero J, Cruts M, van Duijn CM, Van Broeckhoven C (2006). "APP duplication is sufficient to cause early onset Alzheimer's dementia with cerebral amyloid angiopathy". Brain. 129 (Pt 11): 2977–83. doi:10.1093/brain/awl203. PMID 16921174.
^Kohno, T.; Kawanishi, M.; Matsuda, S.; Ichikawa, H.; Takada, M.; Ohki, M.; Yamamoto, T.; Yokota, J. (March 1998). "Homozygous deletion and frequent allelic loss of the 21q11.1-q21.1 region including the ANA gene in human lung carcinoma". Genes, Chromosomes & Cancer. 21 (3): 236–243. doi:10.1002/(sici)1098-2264(199803)21:3<236::aid-gcc8>3.0.co;2-0. ISSN 1045-2257. PMID 9523199. S2CID 24082301.
^Genome Decoration Page, NCBI. Ideogram data for Homo sapience (400 bphs, Assembly GRCh38.p3). Last update 2014-03-04. Retrieved 2017-04-26.
^Genome Decoration Page, NCBI. Ideogram data for Homo sapience (550 bphs, Assembly GRCh38.p3). Last update 2015-08-11. Retrieved 2017-04-26.
^International Standing Committee on Human Cytogenetic Nomenclature (2013). ISCN 2013: An International System for Human Cytogenetic Nomenclature (2013). Karger Medical and Scientific Publishers. ISBN 978-3-318-02253-7.
^Sethakulvichai, W.; Manitpornsut, S.; Wiboonrat, M.; Lilakiatsakun, W.; Assawamakin, A.; Tongsima, S. (2012). "Estimation of band level resolutions of human chromosome images". 2012 Ninth International Conference on Computer Science and Software Engineering (JCSSE). pp. 276–282. doi:10.1109/JCSSE.2012.6261965. ISBN 978-1-4673-1921-8. S2CID 16666470.
^"p": Short arm; "q": Long arm.
^For cytogenetic banding nomenclature, see article locus.
^ a bThese values (ISCN start/stop) are based on the length of bands/ideograms from the ISCN book, An International System for Human Cytogenetic Nomenclature (2013). Arbitrary unit.
^gpos: Region which is positively stained by G banding, generally AT-rich and gene poor; gneg: Region which is negatively stained by G banding, generally CG-rich and gene rich; acenCentromere. var: Variable region; stalk: Stalk.
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Rovelet-Lecrux A, Hannequin D, Raux G, Le Meur N, Laquerriere A, Vital A, Dumanchin C, Feuillette S, Brice A, Vercelletto M, Dubas F, Frebourg T, Campion D (2005). "APP locus duplication causes autosomal dominant early-onset Alzheimer disease with cerebral amyloid angiopathy". Nature Genetics. 38 (1): 24–6. doi:10.1038/ng1718. PMID 16369530. S2CID 559054.
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External links
Wikimedia Commons has media related to Human chromosome 21.
National Institutes of Health. "Chromosome 21". Genetics Home Reference. Archived from the original on 2011-06-05. Retrieved 2017-05-06.
"Chromosome 21". Human Genome Project Information Archive 1990–2003. Retrieved 2017-05-06.