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 (trisomy 21) have Down syndrome.
| Chromosome 21 | |
|---|---|
Human chromosome 21 pair after G-banding. One is from the mother, one is from the father. | |
Chromosome 21 pair in human male karyogram. | |
| Features | |
| Length (bp) | 45,090,682 bp (CHM13) |
| No. of genes | 215 (CCDS) |
| Type | Autosome |
| Centromere position | Acrocentric (12.0 Mbp) |
| Complete gene lists | |
| CCDS | Gene list |
| HGNC | Gene list |
| UniProt | Gene list |
| NCBI | Gene list |
| External map viewers | |
| Ensembl | Chromosome 21 |
| Entrez | Chromosome 21 |
| NCBI | Chromosome 21 |
| UCSC | Chromosome 21 |
| Full DNA sequences | |
| RefSeq | NC_000021 (FASTA) |
| GenBank | CM000683 (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.
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