Human chromosome 10, coloured scanning electron micrograph (SEM). Chromosomes are a packaged form of the genetic material DNA (deoxyribonucleic acid). Each consists of two identical, parallel strands (chromatids, left and right), joined at an area called a centromere (centre). The tips (green) are called telomeres. Humans have 23 pairs of chromosomes. This is chromosome 10, which carries between 800 and 1200 genes. Gene defects on this chromosome are related to diseases such as Usher syndrome, nonsyndromic deafness, and a form of porphyria. Magnification: x25,000 when printed 10 centimetres tall.