chromosome 21 chromosome 21 chromosome 21 is one of the 23 pairs of chromosomes in humans. chromosome 21 is both the smallest human autosome and chromosome, with 45 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 have down syndrome, also called "trisomy 21". chromosome 21human chromosome 21 pair after g-banding.one is from the mother, one is from the father.chromosome 21 pairin human male karyogram.featureslength (bp)45,090,682 bp(chm13)no. of genes215 (ccds)typeautosomecentromere positionacrocentric(12.0 mbp)complete gene listsccdsgene listhgncgene listuniprotgene listncbigene listexternal map viewersensemblchromosome 21entrezchromosome 21ncbichromosome 21ucscchromosome 21full dna sequencesrefseqnc_000021 (fasta) genbankcm000683 (fasta) 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. 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. estimated by protein-coding genes non-coding rna genes pseudogenes source release date ccds212—— 2022-10-26 hgnc215185194 2022-12-23 ensembl234404183 2017-03-29 uniprot252—— 2018-02-28 ncbi256356207 2017-05-19 gene list the following is a partial list of genes on human chromosome 21. for complete list, see the link in the infobox on the right. 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 adarb1: encoding enzyme double-stranded rna-specific editase 1 agpat3: encoding enzyme 1-acyl-sn-glycerol-3-phosphate acyltransferase gamma aire: encoding protein autoimmune regulator app: encoding amyloid beta (a4) precursor protein (peptidase nexin-ii, alzheimer disease) atp5pf: encoding enzyme subunit atp synthase-coupling factor 6, mitochondrial atp5po: encoding enzyme subunit atp synthase subunit o, mitochondrial b3galt5: encoding enzyme beta-1,3-galactosyltransferase 5 bace2: encoding enzyme beta-secretase 2 bach1: encoding transcription factor transcription regulator protein bach1 brwd1: encoding bromodomain and wd repeat-containing protein 1 btg3: encoding protein btg3 c21orf58: encoding uncharacterized protein c21orf58 c21orf62: expressed in tissues of the brain and reproductive organs c21orf91: encoding protein eurl homolog cbr1: encoding enzyme carbonyl reductase 1 cbr3: encoding enzyme carbonyl reductase 3 cbs: encoding enzyme cystathionine-beta-synthase cct8: encoding t-complex protein 1 subunit theta cfap298: encoding cilia- and flagella-associated protein 298 chaf1b: encoding chromatin assembly factor 1 subunit b chodl: encoding chondrolectin, a c-type lectin cldn8: encoding protein claudin-8 cldn14: encoding protein claudin-14 cldn17: encoding protein claudin-17 clic6: encoding chloride intracellular channel protein 6 col6a1: encoding alpha-1 chain of collagen vi col6a2: encoding alpha-2 chain of collagen vi col18a1: encoding alpha-1 chain of collagen xviii cryaa: encoding alpha-crystallin a chain cryzl1: encoing protein crystallin zeta-like 1 cstb: encoding protein cystatin-b cxadr: encoding protein coxsackievirus and adenovirus receptor cyyr1: encoding protein cysteine and tyrosine rich 1 dip2a: disco-interacting protein 2 homolog a dnajc28: encoding protein dnaj homolog subfamily c member 28 dnmt3l: encoding protein dna (cytosine-5)-methyltransferase 3-like dop1b: encoding protein dopey family member 2 dscam: encoding cell adhesion molecule dscam dscr1: down syndrome critical region 1 dyrk1a: dual specificity tyrosine-(y)-phosphorylation regulated kinase 1a erg: encoding protein transcriptional regulator erg ervh48-1: encoding protein suppressyn ets2: encoding protein c-ets-2 fam3b: encoding protein family with sequence similarity 3 member b frgca: producing long non-coding rna foxm1-regulated, gastric cancer associated ftcd: encoding enzyme formimidoyltransferase-cyclodeaminase gabpa: encoding ga-binding protein alpha chain gart: encoding enzyme trifunctional purine biosynthetic protein adenosine-3 gatd3a: encoding glutamine amidotransferase-like class 1 domain-containing protein 3a, mitochondrial grik1: encoding glutamate receptor ionotropic, kainate 1 h2bc12l: encoding histone h2b type f-s hlcs: encoding enzyme holocarboxylase synthetase (biotin-(propionyl-coenzyme a-carboxylase (atp-hydrolysing)) ligase) hmgn1: encoding non-histone chromosomal protein hmg-14 hspa13: encoding heat shock 70 kda protein 13 icoslg: encoding protein icos ligand ifnar1: encoding interferon alpha/beta receptor 1 ifnar2: encoding interferon alpha/beta receptor 2 ifngr2: encoding interferon gamma receptor 2 il10rb: encoding interleukin-10 receptor subunit beta itgb2: encoding protein integrin beta-2 itsn1: encoding protein intersectin-1 jam2: encoding protein junctional adhesion molecule b kcne1: encoding potassium voltage-gated channel, isk-related family, member 1 kcne2: encoding potassium voltage-gated channel, isk-related family, member 2 kcnj6: encoding g protein-activated inward rectifier potassium channel 2 kcnj15: encoding atp-sensitive inward rectifier potassium channel 15 lrrc3: encoding leucine-rich repeat-containing protein 3 lss: encoding enzyme lanosterol synthase ltn1: encoding enzyme e3 ubiquitin-protein ligase listerin map3k7cl: encoding map3k7 c-terminal-like protein mcm3ap: encoding germinal-center associated nuclear protein mir155 producing microrna mir-155 mir3648: producing microrna 3648 mis18a: encoding protein protein mis18-alpha morc3: encoding morc family cw-type zinc finger protein 3 mrap: encoding melanocortin-2 receptor accessory protein mrpl39: encoding 39s ribosomal protein l39, mitochondrial mrps6: encoding 28s ribosomal protein s6, mitochondrial mx1: encoding interferon-induced gtp-binding protein mx1 mx2: encoding interferon-induced gtp-binding protein mx2 n6amt1: n-6 adenine-specific dna methyltransferase 1 ndufv3: encoding nadh dehydrogenase flavoprotein 3, mitochondrial nrip1: nuclear receptor-interacting protein 1 olig1: encoding oligodendrocyte transcription factor 1 olig2: encoding oligodendrocyte transcription factor 2 paxbp1: encoding protein gc-rich sequence dna-binding factor homolog pcbp3: encoding poly(rc)-binding protein 3 pcnt: encoding protein centrosomal pericentrin pcp4: encoding calmodulin regulator protein pcp4 pde9a: encoding enzyme high affinity cgmp-specific 3',5'-cyclic phosphodiesterase 9a pdxk: encoding enzyme pyridoxal kinase pfkl: encoding enzyme atp-dependent 6-phosphofructokinase, liver type pigp: encoding phosphatidylinositol n-acetylglucosaminyltransferase subunit p pknox1: encoding homeobox protein pknox1 pofut2: encoding enzyme gdp-fucose protein o-fucosyltransferase 2 prdm15: encoding pr domain zinc finger protein 15 prmt2: encoding enzyme protein arginine n-methyltransferase 2 psmg1: encoding protein proteasome assembly chaperone 1 pttg1ip: encoding pituitary tumor-transforming gene 1 protein-interacting protein pwp2: encoding periodic tryptophan protein 2 homolog rbm11: encoding protein splicing regulator rbm11 ripk4: encoding enzyme receptor-interacting serine/threonine-protein kinase 4 rnr4: rna, ribosomal 45s cluster 4 rrp1: encoding protein ribosomal rna processing protein 1 homolog a rrp1b: encoding protein ribosomal rna processing 1 homolog b rsph1: encoding protein radial spoke head 1 homolog runx1: encoding protein runt-related transcription factor 1 rwdd2b: encoding protein rwd domain-containing protein 2b s100b: encoding calcium binding protein samsn1: encoding sam domain-containing protein samsn-1 sh3bgr: encoding sh3 domain-binding glutamic acid-rich protein sik1: encoding serine/threonine-protein kinase sik1 sim2: encoding protein single-minded homolog 2 slc5a3: encoding protein sodium/myo-inositol cotransporter slc19a1: encoding protein reduced folate transporter slc37a1: encoding glucose-6-phosphate exchanger slc37a1 smim11: encoding small integral membrane protein 11 sod1: encoding enzyme superoxide dismutase 1, soluble (amyotrophic lateral sclerosis 1 (adult)) son: encoding protein son spatc1l: encoding protein spatc1l sumo3: encoding protein small ubiquitin-related modifier 3 synj1: encoding protein synaptojanin-1 tcp10l: encoding t-complex protein 10a homolog 1 tff1: encoding protein trefoil factor 1 tff2: encoding protein trefoil factor 2 tff3: encoding protein trefoil factor 3 tiam1: rho guanine nucleotide exchange factor tiam1 tmem1: encoding protein encoding protein encoding protein trafficking protein particle complex subunit 10 tmprss2: encoding enzyme transmembrane protease serine 2 tmprss3: encoding enzyme transmembrane protease, serine 3 tmprss15: encoding enteropeptidase tpte: encoding protein putative tyrosine-protein phosphatase tpte trpm2: encoding protein transient receptor potential cation channel subfamily m member 2 ttc3: encoding protein tetratricopeptide repeat domain 3 u2af1: encoding splicing factor u2af 35 kda subunit ubash3a: encoding ubiquitin-associated and sh3 domain-containing protein a ube2g2: encoding ubiquitin-conjugating enzyme e2 g2 umodl1-as1: producing long non-coding rna usp16: encoding enzyme ubiquitin carboxyl-terminal hydrolase 16 usp25: encoding enzyme ubiquitin carboxyl-terminal hydrolase 25 wdr4: encoding trna (guanine-n(7)-)-methyltransferase non-catalytic subunit wdr4 zbtb21: encoding zinc finger and btb domain-containing protein 21 diseases and disorders the following diseases and disorders are some of those related to genes on chromosome 21: alzheimer's disease amyotrophic lateral sclerosis atrial fibrillation, familial autoimmune polyendocrine syndrome basal ganglia calcification bethlem myopathy closed angle glaucoma cataract down syndrome erondu–cymet syndrome holocarboxylase synthetase deficiency homocystinuria hyperhomocysteinemia hypotrichosis immunodeficiency inflammatory bowel disease intellectual developmental disorder jervell and lange-nielsen syndrome keppen–lubinsky syndrome leukocyte adhesion deficiency-1 majewski osteodysplastic primordial dwarfism type ii (mopd ii, or mopd2) non-small cell lung carcinoma nonsyndromic deafness peripheral neuropathy primary ciliary dyskinesia romano–ward syndrome ullrich congenital muscular dystrophy unverricht–lundborg disease, a form of progressive myoclonus epilepsy chromosomal conditions a karyotype of somebody affected with down syndrome, depicting the presence of a full additional copy of chromosome 21. the presence of this extra copy is also referred to as trisomy 21. 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.) and a dutch family set. 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 21g-banding ideogram of human chromosome 21 in resolution 850 bphs. band length in this diagram is proportional to base-pair length. this type of ideogram is generally used in genome browsers (e.g. ensembl, ucsc genome browser).g-banding patterns of human chromosome 21 in three different resolutions (400, 550 and 850). band length in this diagram is based on the ideograms from iscn (2013). this type of ideogram represents actual relative band length observed under a microscope at the different moments during the mitotic process. g-bands of human chromosome 21 in resolution 850 bphs chr. arm band iscnstart iscnstop basepairstart basepairstop stain density 21p 13031113,100,000 gvar 21p 123116833,100,0017,000,000 stalk 21p 11.268310567,000,00110,900,000 gvar 21p 11.11056127410,900,00112,000,000 acen 21q 11.11274136712,000,00113,000,000 acen 21q 11.21367158413,000,00115,000,000 gneg 21q 21.11584201915,000,00122,600,000 gpos100 21q 21.22019214422,600,00125,500,000 gneg 21q 21.32144233025,500,00130,200,000 gpos75 21q 22.112330248530,200,00134,400,000 gneg 21q 22.122485261034,400,00136,400,000 gpos50 21q 22.132610270336,400,00138,300,000 gneg 21q 22.22703285838,300,00141,200,000 gpos50 21q 22.32858320041,200,00146,709,983 gneg