Human chromosome 1. Coloured scanning electron micrograph (SEM) of human chromosome 1. Humans have 23 pairs of chromosomes, this is the largest. It accounts for 10% of the human genome. Chromosomes, which consist of two identical chromatids joined at a centromere, are comprised of deoxyribonucleic acid (DNA) and proteins. DNA contains sections, called genes, which encode the body's genetic information. The Human Genome Project has identified the function of some of chromosome 1's genes. On chromosome 1 is a gene responsible for the eye disease glaucoma, one of the genes implicated in Alzheimer's disease and a gene for susceptibility to prostate cancer. Magnification: x16,800 when printed 10cm wide.