Human chromosomes. Coloured scanning electron micrograph (SEM) of condensed human chromosomes. Humans have 23 pairs of chromosomes in the nucleus of almost all cells. One chromosome of each pair comes from the mother, the other from the father. Chromosomes, which consist of two identical chromatids joined at a centromere, are comprised of deoxyribonucleic acid (DNA) coiled around proteins. DNA contains sections, called genes, which encode the body's genetic information, determining each cell's structure, function and behaviour. Magnification: x5,700 when printed 10 centimetres wide.