- a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes.
Each chromosome consists of a DNA double helix bearing a linear sequence of genes, coiled and recoiled around aggregated proteins (histones). Their number varies from species to species: humans have 22 pairs plus the two sex chromosomes (two X chromosomes in females, one X and one Y in males). During cell division, each DNA strand is duplicated, and the chromosomes condense to become visible as distinct pairs of chromatids joined at the centromere. Bacteria and viruses lack a nucleus and have a single chromosome without histones
late 19th century: coined in German from Greek khrōma 'color' + sōma 'body'