Chromosome 1

Size: 249 Mb (million base pairs)
Approx. no. of genes: 2400

Chromosome 1 is the largest human chromosome and contains the largest number of genes. The number of genes located on chromosome 1 makes up about 10% of the entire human genome. The chromosome is metacentric (the centromere is in the middle so that the arms are about the same length) and there is a large heterochromatin region (condensed and inactive DNA segment) located near the centromere on the long arm. Chromosome 1 contains three large clusters of ribosomal RNA genes. Gene density (11 genes per Mb) and content of GC pairs (42%) are above the genomic average (9-10 genes per Mb and 41%, respectively). It contains a relatively small proportion of repeat sequences compared to the human genome as a whole.