Chromosome 5 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 5 spans about 181 million base pairs (the builing blocks of DNA) and represents almost 6% of the total DNA in cells. Chromosome 5 is one of the largest human chromosomes, yet has one of the lowest gene densities. This is partially explained by numerous gene-poor regions that display a remarkable degree of noncoding and syntenic conservation with non-mammalian vertebrates, suggesting they are functionally constrained.