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  • Open Access

Sequence of human chromosome 21

Genome Biology20001:spotlight-20000509-01

  • Published:


  • Active Gene
  • Human Gene
  • Human Chromosome
  • Average Gene
  • Gene Density

Chromosome 21 may have as few as 225 active genes in its 33.8 Mb of DNA, according to the sequence published electronically by Nature on May 8 (and published in print on May 18 as Hattori et al. Nature 2000, 405:311-319). This is roughly half the gene density of the only other completely sequenced chromosome arm, that of chromosome 22, and it includes a 7 Mb stretch - larger than the Escherichia coligenome - that contains only one gene. Extrapolating from the average gene density of chromosomes 21 and 22 gives a total number of human genes that is closer to 40,000 than the estimated 70-140,000. The low density of genes on chromosome 21 may explain why children with Down's syndrome, who are trisomic for chromosome 21, can survive.


  1. Nature magazine's homepage, []
  2. The DNA sequence of human chromosome 22Google Scholar


© BioMed Central Ltd 2000