Human chromosomes. Coloured scanning electron micrograph (SEM) of a group of human chromosomes. These structures occur in the nucleus of every cell in the body, carrying genetic information in the form of DNA (deoxyribonucleic acid), arranged in discrete segments known as genes. Apart from the sex cells, every human cell contains 46 chromosomes, 23 inherited from the father and 23 from the mother. The chromosomes shown here have replicated themselves during cell division and so consist of two identical strands (chromatids) linked at their centre by a structure known as a centromere. Magnification: x6000 at 6x7cm size.