DNA replication. Conceptual computer artwork representing DNA (deoxyribonucleic acid) replication. A zip is seen splitting one strand (lower left) into two. An autoradiogram (genetic fingerprint) and a bar code are seen in the background. DNA comprises two spiral sugar- phosphate strands (purple) linked by four types of base (red/green/blue/yellow). Each base only links with one other, so one strand is complementary to the other. When DNA divides, the strands split and each makes an exact copy of its original partner by building up the complementary sequence of bases. DNA is found in all living things and controls growth and development.