Chromosome with DNA, computer artwork. Chromosomes are the structures in cells that carry the DNA (deoxyribonucleic acid) genetic material. DNA exists as a double helix, with two sugar-phosphate strands (yellow) spiralling round each other, linked by the interactions between bases (red and blue) between them. The sequence of bases encodes a recipe for making a specific protein. Chromosomes normally exist as long strands, but condense into X-shaped structures such as this during cell division. Each chromosome comprises two identical chromatids linked at the centromere. During replication, the chromatids separate to become two new identical chromosomes.