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Chromosome 21 is one of the 23 pairs of chromosomes in humans. People without Down syndrome have two copies of this chromosome. The trisomy of the 21st chromosome causes Down syndrome. Chromosome 21 is the smallest human chromosome, with 48 million nucleotides (the building material of DNA) representing about 1.5 percent of the total DNA in cells. In 2000, researchers working on the Human Genome Project announced 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. Identifying genes on each chromosome is an active area of genetic research. However, because researchers use different approaches to predict the number of genes on each chromosome, the estimated number of genes varies. Depending on the genome annotation used, chromosome 21 contains 477 or 635 genes.〔(【引用サイトリンク】 publisher=National Center for Biotechnology Information )〕〔(【引用サイトリンク】 publisher=Wellcome Trust Sanger Institute )〕 ==Genes== The following are some of the genes located on chromosome 21: * APP: amyloid beta (A4) precursor protein (peptidase nexin-II, Alzheimer disease) * C21orf59: Chromosome 21 open reading frame 59 * CBS: cystathionine-beta-synthase * CLDN14: claudin 14 * HLCS: holocarboxylase synthetase (biotin-(propionyl-Coenzyme A-carboxylase (ATP-hydrolysing)) ligase) * KCNE1: potassium voltage-gated channel, Isk-related family, member 1 * KCNE2: potassium voltage-gated channel, Isk-related family, member 2 * LAD: leukocyte adhesion deficiency (symbols are ITGB2, CD18, LCAMB) * SOD1: superoxide dismutase 1, soluble (amyotrophic lateral sclerosis 1 (adult)) * TMPRSS3: transmembrane protease, serine 3 * PCNT: centrosomal pericentrin * DSCR1: Down Syndrome critical region 1 * DYRK1A: dual specificity tyrosine-(Y)-phosphorylation regulated kinase 1A * RRP1B: ribosomal RNA processing 1 homolog B * S100B: calcium binding protein 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chromosome 21 (human)」の詳細全文を読む スポンサード リンク
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